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Fabrication and Characterization of Low Cost Electrodes for Fuel Cells

Ph.D. Thesis

Ghazanfar Abbas

Department of Physics Bahauddin Zakariya University

Multan-60800, Pakistan 2011

Fabrication and Characterization of Low Cost Electrodes for Fuel Cells

Ph.D. Thesis

Ghazanfar Abbas

This dissertation is submitted to the Department of Physics,

Bahauddin Zakariya University, Multan (BZU) in partial fulfillment

of the requirement for the degree of Ph.D. in Physics

Department of Physics Bahauddin Zakariya University

Multan 60800, Pakistan 2011

In The Name of ALLAH Who is The Most Merciful and the Most Beneficent

I

Deceleration of Originality

I herby declare that the work contained in this dissertation and the intellectual

contents of this dissertation are the product of my own work. The thesis entitled

“Fabrication and Characterization of Low Cost Electrode for Fuel Cells” for the

award of Ph.D. Degree in Physics has not been submitted to any university within

Pakistan or abroad. This thesis has neither been previously published in any form nor

does it contain any verbatim of the published resources which could be treated as

infringement of the international copy right law.

I also declare that I do understand the terms “copy right” and “plagiarism”. In

case of any copy right violation and plagiarism found in this work, I will be held fully

responsible of the consequences of any such violation.

Dated: July 29, 2011 Signature ----------------

Ghazanfar Abbas,

Ph. D. Scholar, Department of Physics, Bahauddin Zakariya University, Multan-60800, Pakistan

II

CERTIFICATE

This is to certify that I have read this thesis entitled “Fabrication and

Characterization of Low Cost Electrodes for Fuel Cells” written by Mr. Ghazanfar

Abbas, in my opinion it is fully adequate in scope and quality for the award of Ph.D.

degree in Physics [ Renewable Energy (Fuel Cell) Technology].

Approved by ------------------------------------------ Prof. Dr. Muhammad Ashraf Chaudhry, Professor, Department of Physics, Bahauddin Zakariya University, Multan 60800, Pakistan

III

List of Publications Included in Thesis

A) Published

1 Ghazanfar Abbas, Rizwan Raza, M. Ashraf Chaudhry, Bin Zhu, “Preparation

and Characterization of Nanocomposite Calcium Doped Ceria Electrolyte

with Alkali Carbonates (NK-CDC) for SOFC.” Journal of Fuel Cell Science

and Technology, Vol. 8, Issue 4, (2011); Page: 041013.

2 Rizwan Raza, Ghazanfar Abbas, S. Khalid Imran, Imran Petal, Bin Zhu,

“GDC-Y2O3 Oxide Based Two Phase Nanocomposite Electrolyte.” Journal of

Fuel Cell Science and Technology, Vol. 8, Issue 4, (2011); Page 041012.

3 Ghazanfar Abbas,M, Ashraf Chaudhry,Rizwan Raza, Bin Zhu. “Study of

CuNiZnGdCe Nanocomposite Anode for Low Temperature SOFC.”

Nanoscience and Nanotechnology Letters, Vol. 4, (2012): Pages 389-393.

B) Submitted

4 Ghazanfar Abbas, Rizwan Raza, M. Asharf Chaudhry, M. Ajmal Khan,

Richard Ljungberg, Bin Zhu.“Preparation and Characterization of

Nanocomposite Anode (Al0.10 Ni0.50Zn0.40-GDC) for LTSOFC.”Chemical

Engineering Journal.

5 Ghazanfar Abbas, M, Ashraf Chaudhry, Rizwan Raza, M. Ajmal Khan, Bin

Zhu. “Synthesis and Electrochemical Characterization of New Nanoceramics

Ba0.05Cu0.25Fe0.10Zn0.60 (BCFZ) Electrode for LTSOFC”. International Journal

of Energy Research.

6 Ghazanfar Abbas, Rizwan Raza, M. Ashraf Chaudhry, Ashfaq Ahmad, M.

Ajmal Khan, Bin Zhu. “Electrochemical investigation of nanocomposite

mixed metal oxideanode for low temperature solid oxide fuel cell.” Journal of

Power Sources.

7 Ghazanfar Abbas, Rizwan Raza, M. Ajmal Khan, M.Asharf Chaudhry,Bin

Zhu. “Synthesis, Electrical and Electrochemical Properties of Ba0.4

Sr0.6Co0.3Mn0.7O3−δCathode for Low Temperature Solid Oxide Fuel Cells.”

International Journal of Hydrogen Energy.

IV

Additional Publications

8 Rizwan Raza, Ghazanfar Abbas, Xiaodi Wang, Ying Ma, Bin Zhu,

“Electrochemical Study of the Composite Electrolyte Based on Samaria-

Doped Ceria and Containing Yttria as a Second Phase.” Solid State Ionics,

Vol. 188, Issue 1, (2011); Pages: 58-63.

9 Haiying Qin, Zhigang Zhu, Qinghua Liu, Yifu Jing, Rizwan Raza, Syedkhalid

Imran, Manish Singh, Ghazanfar Abbas, Bin Zhu, “Direct Biofuel Low-

Temperature Solid Oxide Fuel Cells.” Energy and Environmental Science,

Vol. 4, Issue 4, (2011); Pages: 1273-1276.

10 Bin Zhu, Rizwan Raza, Ghazanfar Abbas,Manish Singh. “An Electrolyte-

Free Fuel Cell Constructed with One Homogenous Layer with Mixed

Conductivities” Advanced Functional Materials, Vo. 21, Issue 13, (2011);

Pages: 2465-2469.

11 Syed Khalid Imran, Rizwan Raza, Ghazanfar Abbas, Bin Zhu. “Preparation

and Characterization and Development of Bio-ethanol Solid Oxide Fuel Cell.”

Journal of Fuel Cell Science and Technology, Accepted (2011); Paper in

Production of Journal. Vo. 8, Issue 6, (2011); Pages 061014.

12 Rizwan Raza, Ghazanfar Abbas, Bin Zhu, “La0.3Sr0.2Mn0.1Zn0.4 oxide -

Sm0.2Ce0.8O1.9 (LSMZ-SDC) Nanocomposite cathode for Low Temperature

SOFCs”,Journal of Nanoscience and Nanotechnology, Vol. 12, Issue 6, (2012), Pages 4994-4997.

Papers Presented in International Conferences

1) Ghazanfar Abbas, Rizwan Raza,M, Ashraf Chaudhry, M. Ajmal Khan, Bin

Zhu. “Electrochemical Investigation of Nanocomposite Mixed Metal

OxideAnode for Low Temperature Solid Oxide Fuel Cell.” 9th ISSFIT

International Symposium on Systems with Fast Ionic Transport, 1-5 June 2010,

Riga, Latvia.(Funded by GETT Fuel Cell Lab. Stockhom, Sweden).

2) Ghazanfar Abbas, M, Ashraf Chaudhry, Rizwan Raza, M. Ajmal Khan, Bin

Zhu. “Synthesis and Electrochemical Characterization of New Nano-structured

BCFZ Electrode for LTSOFC.” Workshop, September 17, 2010, Helsinki,

Finland. (Funded by GETT Fuel Cell Lab. Stockhom, Sweden).

V

3) Ghazanfar Abbas, Rizwan Raza, M.Asharf Chaudhry, M. Ajmal Khan, S.

Khalid Imran, Richard Ljungberg, Bin Zhu.“Preparation and

Characterization of Nanocomposite Anode (Al0.1Ni0.5Zn0.4-GDC) for

LTSOFC.” 5th NANOSMAT Conference, 19-22 October, 2010, Reims,

France. (Funded by Higher Education Commission, (HEC) Pakistan).

International Conferences Proceedings

4) Ghazanfar Abbas,Rizwan Raza, M. Ashraf Ch. and B. Zhu“Preparation and

Characterization of Nanocomposite Calcium Doped Ceria Electrolyte with

Alkali Carbonates (Nk-CDC) for SOFC” Published in the Proceedings of the

8th International Fuel Cell Science, Engineering and Technology, June 14-

16, 2010, Brooklyn, New York, USA.

5) Rizwan Raza,Ghazanfar Abbas and Bin Zhu,“GDC-Y2O3 Oxide Based Two

Phase Nanocomposite Electrolytes”Published in the Proceedings of the 8th

International Fuel Cell Science, Engineering and Technology, June 14-16,

2010, Brooklyn, New York, USA.

6) Rizwan Raza, Ghazanfar Abbas, Xiaodi Wang, Ying Ma and B. Zhu, “The

Electrochemical Study of Oxides Coated @Doped Ceria”Published in the

Proceeding of 9th ISSFIT, 1-5 June 2010, Riga (Latvia).

7) Rizwan Raza, Ghazanfar Abbas, Imran Petal, Bin Zhu, "La0.3Sr0.2Mn0.1Zn0.4

Oxide- Sm0.2Ce0.8O1.9 (LSMZ-SDC) Nanocomposite Cathode for Low

Temperature SOFCs"Proceeding in 5th NANOSMAT conference, 19-21

October 2010, Reims, FRANCE.

Website - www.nanosmat-conference.com

VI

ACKNOWLEDGMENTS All praise for ALMIGHTY ALLAH, who is the creator of the entire universe.

All things that lie in the universe are the property of the most beneficent and the most merciful ALLAH, who is the most promising, the most generous and supreme ruler. It is He, whose blessing and glory flourished my thoughts and fulfilled my ambitions and dreams. It will be a great honor for me if I pray to His beloved MUHAMMAD (S.A.W) because this universe was established with the great concept of MUHAMMAD (S.A.W.). I will never forget to admire the holy family of MUHAMMAD (S.A.W.). ALL-E-MUHAMMAD is the unique family who has survived the Islam for Muslim community by offering blood and wealth sacrifices.

I always pay a lot of thanks to ALLAH, who has gifted me nice, honorable, intelligent and intellectual teachers for my guidance to achieve knowledge and skill. At the first and foremost, I would like to express profound gratitude to my supervisor, Prof. Dr. Muhammad Ashraf Chaudhry, Department of Physics, BZU Multanfor providing me an opportunity to join the Department of Physics, Bahauddin Zakariya University, Multan. His continuous encouragement and tremendous efforts enabled me to complete the research work successfully.

I express a lot of thanks to my external supervisor, Prof. Dr. Bin Zhu, KTH, Stockholm, Sweden, who has in fact facilitated me in his GETT Fuel Cell Lab. KTH, Sweden and trained me to work and helped me during my stay in Sweden. His enormous efforts and timely help spurred me to complete the research work. I wish him a great success in his scientific carrier and a happy family life.

My deep appreciations are every time available to Prof. Dr. Ejaz Ahmad, Chairman, Department of Physics, Bahauddin Zakariya University (BZU), Multan for providing me the research facilities through out the study.

I am very grateful to Dr. Misbah-ul-Islam, Dr. Javed Ahmad, Department of Physics, and Prof. Dr. Bashir Ahmad Ch., Focal Person HEC, Department of Pharmacy, Bahauddin Zakariya University, (BZU), Multan for their academic and experimental support.

With great veneration, I will just say about my friend Dr. Rizwan Raza, Assistant Professor, Department of Physics, CIIT Lahore that I am unable to give him credit for his kind scientific and moral support. Because of his scientific inclination, I will say that he is a man of science and it is not a superstitious proposition. I will pay my special thanks to Dr. Majid Muneer, Assistant Professor, G. C. University, Faislabad and Prof. Dr. M. Yousaf Hussain, Chairman, Department of Physics, University of Agriculture, Faisalabad for their continuous support during my work. I wish for them great success in their scientific goals and a happy family life.

I express numerous appreciations to my GETT Fuel Cell Lab.Colleagues Richard Ljungberg, Haiying Qin, Zhigang Zhu, Qinghua Liu, Yifu Jing, Fan, Manish Singh, Xiaodi Wang and Ying Ma for learning experimental knowledge and techniques.

Special thanks to Higher Education Commission (HEC), Pakistan for providing me indigenous scholarship for four years alongwith a six month foreign

VII

training under International Research Support Initiative Program (IRSIP). In fact, this program is highly beneficial to the indigenous scholars for experiencing an international exposure.

I would pay special gratitude to Dr. S. M. Junaid Zaidi, Rector, CIIT, Prof. Dr. Arshad Saleem Bhatti, Dean, Faculty of Sciences, Prof. Dr. Ishaq Ahmad, Head of Physics Department, COMSATS Institute of Information Technology, Islamabad for providing me a study leave to complete my Ph.D. Degree.

I am very thankful to Bashir Ahmad, laboratory Superintendent for his continuous acquaintance and support to provide me Lab. instruments and equipments during my research work. I am also thankful to Fida Hussain Sajid, Abd-ul-Sattar Muhammad Ayub, Ejaz Ahmad, Sajjad Akhter and Muhammad Ali for technical support and office management activities. Kind help of Sh. Riaz Ahmad,Ghulam Ali and Akhter Rasul,Account Department, BZU, Multan is also acknowledged.

I would like to say many thanks to my research fellows Mr. Muhammad Ajmal Khan and Ms. Khair-un-Nisa for their academic, experimental and technical support during my whole study.I render many thanks to my co-operative and sincere friends and class fellows Muhammad Kamran Tahir Malik, Mukhtar Ahmad, Imran Ahmad, Shafique Anwar, Muhammad Saleem Abid, Mehtab Ullah, Sabir Hussain, Farooq Wasiq and Faiza Aenfor their fruitful academic as well as technical discussions during my research work. Special thanks to all the rest of my colleagues’ seniors and juniors for their sincere help and encouragement.

I will never forget my closest friends Mujahid Abbas, Mazhar Abbas, Muhammad Ali Khawar, Malik Iftejhar Jafar, Fayyaz-ul-Hasan Bhatti, Iftekhar Ahmad Ghori and Naeem Ahmad Ch. for their encouraging motivation.

I offer great thanks to my family friends Mian Muhammad Aslam, Sub-Engineer,Building Department, Khanewal,Mian Muhammad Ramzan, Consultant Engineer,Indus Dying and Manufacturing Company, Karachi,Mian Muhammad Yasin, Mian Iqbal Hussain, State Life Com. (T. T. Singh)and Mian Mazhar Abbas, (Dawlance Com. Multan) for their endless assistance, valuable suggestions and love not only for my academic carrier yet for every matter of my life.

At the last but not the least, I present countless thanks to my affectionate and adoring mother, aunt, brother Mian Akhtar Abbas and blind love to my respectable sister for their fearlessness and unlimited hardworking. I appreciate my family who has faced a lot of financial problems in handling domestic’s issues during my studies.

I propose earnest and devout appreciations to my wife Asma Ghazanfar, for her cooperation, who exhibited a prolonged patience for my study and whose hands always raisedfor prayers for my success.

Cordial love to my sweet kids AROOJ FATIMAAROOJ FATIMAAROOJ FATIMAAROOJ FATIMA, MIAN AZEEM, MIAN AZEEM, MIAN AZEEM, MIAN AZEEM----ULULULUL----HASAN HASAN HASAN HASAN

ANDMIAN MIAN MIAN MIAN SAFEERSAFEERSAFEERSAFEER----ULULULUL----HUSHUSHUSHUSSASASASAIIIINNNN.

I pray for health and long life of all my well wishers and companions.

Signature ----------------------- Mian Ghazanfar Abbas,

VIII

Table of Contents

ABSTRACT XX

Chapter No. 1 1

1 INTRODUCTION ----------------------------------------------- 2

1.1 Importance ---------------------------------------------------------------------------- 2

1.2 Non Renewable Energy Sources --------------------------------------------------- 2

1.3 Renewable Energy Sources --------------------------------------------------------- 2

1.3.1 Water -------------------------------------------------------------------------------- 2

1.3.2 Solar --------------------------------------------------------------------------------- 3

1.3.3 Wind --------------------------------------------------------------------------------- 3

1.3.4 Geothermal ------------------------------------------------------------------------- 3

1.3.5 Biomass ----------------------------------------------------------------------------- 4

1.3.6 Alternative Energy Sources ------------------------------------------------------ 4

1.4 Fuel Cells ------------------------------------------------------------------------------ 4

1.4.1 Types of Fuel Cells ------------------------------------------------------------------ 5

1.4.1.1 Alkaline Fuel Cells (AFCs) ----------------------------------------------------- 6

1.4.1.2 Phosphoric Acid Fuel Cells (PAFCs) ----------------------------------------- 7

1.4.1.3 Molten Carbonate Fuel Cells (MCFCs) -------------------------------------- 7

1.4.1.4 Proton Exchange Membrane Fuel Cells (PEMFCs) ------------------------ 8

1.4.1.5 Solid Oxide Fuel Cells (SOFCs) ----------------------------------------------- 9

1.5 How SOFC Works ------------------------------------------------------------------- 12

1.6 Construction of Solid Oxide Fuel Cell (SOFC) ---------------------------------- 14

1.6.1 Anode ------------------------------------------------------------------------------ 15

1.6.1.1 Composite Anode ----------------------------------------------------------------- 15

1.6.1.2 Nanocomposite Anode ----------------------------------------------------------- 15

1.6.1.2.1 Catalytic Activity -------------------------------------------------------------- 16

1.6.1.2.2 Conductivity -------------------------------------------------------------------- 16

1.6.1.2.3 Open Circuit Voltage (OCV) ------------------------------------------------- 17

1.6.1.2.4 Compatibility ------------------------------------------------------------------- 17

1.6.1.2.5 Porosity ------------------------------------------------------------------------- 17

1.6.1.2.6 Stability ------------------------------------------------------------------------- 17

1.6.2 Electrolyte -------------------------------------------------------------------------- 19

IX

1.6.3 Cathode ----------------------------------------------------------------------------- 19

1.7 Hydrogen as Fuel ------------------------------------------------------------------- 19

1.8 Fuel Cell Applications ---------------------------------------------------------------- 20

1.8.1 Fuel Cells for Stationary Applications ---------------------------------------- 20

1.8.2 Fuel Cells for Mobile Applications -------------------------------------------- 21

1.8.3 Fuel Cells for Portable Applications ------------------------------------------ 21

1.9 Electrochemistry of Solid Oxide Fuel Cell ----------------------------------------- 22

1.10 Interest in Study ----------------------------------------------------------------------- 23

1.11 Objectives ------------------------------------------------------------------------------ 24

Reference ------------------------------------------------------------------------------------- 25

Chapter No. 2 33

2 Review of Literature -------------------------------------------- 34

2.1 Introduction ------------------------------------------------------------------------ 34

2.2 Background of Solid Oxide Fuel Cell ------------------------------------------- 34

2.3 Components of Solid Oxide Fuel Cell ------------------------------------------- 35

2.3.1 Review of Anode Component of SOFC ---------------------------------------- 35

2.3.2 Review of Electrolyte Component of SOFC ---------------------------------- 40

2.3.3 Review of Cathode Component of SOFC ------------------------------------- 43

2.3.4 Review of Cost Comparison of Electrode Materials for SOFC------------- 47

References ------------------------------------------------------------------------------------ 48

Chapter No. 3 51

3 Characterization Tools------------------------------------------- 52

3.1 X-Ray Diffraction (XRD) ----------------------------------------------------------- 52

3.1.1 Determination of Crystal Structure -------------------------------------------- 53

3.1.2 Bragg’s Law ---------------------------------------------------------------------- 54

3.2 Scanning Electron Microscopy (SEM) ------------------------------------------ 54

3.2.1 Topography ----------------------------------------------------------------------- 55

3.2.2 Morphology ----------------------------------------------------------------------- 55

3.2.3 Composition ----------------------------------------------------------------------- 55

3.2.4 Crystallographic Information ---------------------------------------------------- 55

3.3 High Resolution Transmission Electron Microscopy (HR TEM) ------------- 56

3.4 Differential Scanning Calorimetery (DSC) -------------------------------------- 57

3.5 AC Electrochemical Impedance Spectroscopy (EIS) --------------------------- 58

3.5.1 Instrumentation for Basic Measurements ------------------------------------ 59

X

References ------------------------------------------------------------------------------------ 60

Chapter No. 4 61

4 Experimental 62

4.1 Introduction -------------------------------------------------------------------------- 62

4.2 Materials and Equipments --------------------------------------------------------- 62

4.2.1 Chemicals ------------------------------------------------------------------------- 62

4.2.2 Price List of the used chemicals----------------------------------------------- 62

4.2.3 Experimental Accessories ------------------------------------------------------ 67

4.3 Identification of Raw Materials for Low Cost Electrodes ----------------- 68

4.4 Preparation Techniques --------------------------------------------------------- 69

4.4.1 Preparation of Anode Materials ---------------------------------------------- 69

4.4.1.1 Sample No. 1 ---------- CuNiZnGdCe (CNZGC) ---------------------- 69

4.4.1.2 Sample No. 2 (a-e) ---------- Al0.1NixZn0.9-x (ANZ) -------------------- 70

4.4.1.3 Sample No. 3 ---------- Cu0.20Mn0.20Zn0.60 (CMZ) --------------------- 70

4.4.1.4 Sample No. 4 (a-e) ---------- Ba0.05Cu0.25FexZn0.7-x (BCFZ) --------- 71

4.4.1.5 Sample No. 5 ---------- Ba0.15Fe0.10Ti0.15Zn0.60 (BFTZ) ---------------- 71

4.4.2 Preparation of Electrolyte Materials ----------------------------------------- 71

4.4.2.1 Sample No. 6- Sodium-Potassium Carbonated

Calcium Doped Ceria (NK-CDC) --------------------------------------- 71

4.4.2.2 Sample No. 7- Gadolinium Doped Ceria Coated with

Yttrium Oxide (GDC-Y2O3) ----------------------------------------------- 72

4.4.2.3 Sample No. 8- Sodium-Potassium Carbonated

Samarium Doped Ceria (NK-SDC) -------------------------------------- 73

4.4.2.4 Sample No. 9-Sodium Carbonated Samarium Doped Ceria (NSDC)73

4.4.2.5 Sample No. 10- Gadolinium Doped Ceria (GDC) -------------------- 74

4.4.3 Preparation of Cathode Materials -------------------------------------------- 74

4.4.3.1 Sample No. 11 ---------- Ba0.4 Sr0.6Co0.3Mn0.7 (BSCM) --------------- 74

4.4.3.2 Sample No. 12 ---------- La0.1Sr0.9Co0.2Zn0.8 (LSCZ) ------------------ 74

4.4.3.3 Sample No. 13 ---------- Ba0.5Sr0.5Co0.2Fe0.8 (BSCF) ----------------- 75

4.5 Preparation of Composite Anode and Cathode Materials -------------------- 79

4.6 Characterization of Samples ------------------------------------------------------ 80

4.6.1 X-Ray Diffraction ---------------------------------------------------------------- 80

4.6.2 Microscopic Analysis ------------------------------------------------------------ 80

XI

4.6.2.1 Scanning Electron Microscopy (SEM) ---------------------------------- 80

4.6.2.2 Transmission Electron Microscopy (TEM) ----------------------------- 80

4.6.3 Differential Scanning Calorimetery (DSC) ---------------------------------- 81

4.6.4 AC Electrochemical Impedance Spectroscopy (EIS) ----------------------- 81

4.7 Construction of Pellets for Conductivity Measurements ----------------------- 81

4.7.1 Calculation of Activation Energy (Ea) ---------------------------------------- 82

4.8 Construction of Solid Oxide Fuel Cell ------------------------------------------- 82

4.9 Fuel Cell Performance ------------------------------------------------------------ 85

References ------------------------------------------------------------------------------------- 86

Chapter No. 5 87

5 Results and Discussion 88

5.1 Sample No. 1 ---------- CuNiZnGdCe (CNZGC) ------------------------------- 88

5.1.1 Introduction ---------------------------------------------------------------- 88

5.1.2 Structural Studies --------------------------------------------------------- 88

5.1.3 Experimental Setup ------------------------------------------------------- 90

5.1.4 Conductivity Measurements --------------------------------------------- 90

5.1.5 Performance Measurements --------------------------------------------- 92

5.1.6 Calculation of Activation Energy (Ea) --------------------------------- 93

5.1.7 XRD Patterns and Performance of Dry-7 Sintered at

Various Temperatures ----------------------------------------------------- 95

5.1.8 Cost Analysis---------------------------------------------------------------- 97

5.19 Conclusions ----------------------------------------------------------------- 97

5.2 Sample No. 2 (a-e) ---------- Al0.1NixZn0.9-x (ANZ) ---------------------------- 98

5.2.1 Introduction ----------------------------------------------------------------- 98

5.2.2 Structural Studies ---------------------------------------------------------- 98

5.2.3 Microstructure View (Scanning Electron Microscopy) SEM -------- 100

5.2.4 Conductivity Measurements ---------------------------------------------- 101

5.2.5 Calculation of Activation Energy (Ea) ---------------------------------- 103

5.2.6 AC Electrochemical Impedance Spectroscopy (EIS) Analysis ----- 106

5.2.7 Performance Measurements ---------------------------------------------- 107

5.2.8 Cost Analysis--------------------------------------------------------------- 108

5.2.9 Conclusions ----------------------------------------------------------------- 109

5.3 Sample No. 3 ---------- Cu0.20Mn0.20Zn0.60 (CMZ) ----------------------------- 110

5.3.1 Introduction ----------------------------------------------------------------- 110

XII

5.3.2 XRD Patterns --------------------------------------------------------------- 110

5.3.3 SEM Analysis --------------------------------------------------------------- 111

5.3.4 Conductivity Measurements ---------------------------------------------- 112

5.3.5 Calculation of Activation Energy (Ea) ---------------------------------- 113

5.3.6 AC Electrochemical Impedance Spectroscopy (EIS) ----------------- 115

5.3.7 Conductivities of Mixed Electrodes ------------------------------------- 116

5.3.8 Performance of Mixed Electrodes --------------------------------------- 117

5.3.9 Cost Analysis--------------------------------------------------------------- 119

5.3.10 Conclusions ---------------------------------------------------------------- 120

5.4 Sample No. 4 (a-f) ---------- Ba0.05Cu0.25FexZn0.7-x (BCFZ) ------------------ 121

5.4.1 Introduction ---------------------------------------------------------------- 121

5.4.2 Crystallographic Analysis ------------------------------------------------ 121

5.4.3 Scanning Electron Microscopy (SEM) ---------------------------------- 123

5.4.4 Electrical Conductivity Measurements --------------------------------- 124


5.4.6 Electrochemical Impedance Spectroscopy (EIS) --------------------- 128

5.4.7 Fuel Cell Performance Measurements --------------------------------- 133

5.4.8 Stability Measurement ---------------------------------------------------- 135

5.4.9 Cost Analysis---------------------------------------------------------------- 137

5.4.10 Conclusions ---------------------------------------------------------------- 138

5.5 Sample No. 5 ---------- Ba0.15Fe0.10Ti0.15Zn0.60 (BFTZ) ---------------------- 139

5.5.1 Introduction ---------------------------------------------------------------- 139

5.5.2 Crystallographic Analysis ----------------------------------------------- 139

5.5.3 Electrical Conductivity Measurements -------------------------------- 140



5.5.6 Cost Analysis--------------------------------------------------------------- 145

5.5.7 Conclusions ---------------------------------------------------------------- 146

5.6 Sample No. 6- Sodium-Potassium Carbonated Calcium Doped Ceria

(NK-CDC) Electrolyte ------------------------------------------------------------- 147

5.7 Sample No. 7- Yttrium Oxide Coated Gadolinium Doped Ceria

(GDC-Y2O3)------------------------------------------------------------------------- 148

5.8 Sample No. 10 ---------- Sr0.6Ba0.4Co0.3Mn0.7O3-δ (BSCM) ------------------ 149

XIII

5.8.1 Introduction ---------------------------------------------------------------- 149

5.8.2 X-Ray Diffraction Pattern ----------------------------------------------- 149

5.8.3 Scanning Electron Microscopic (SEM) View ------------------------- 150

5.8.4 DC Conductivity Measurements ---------------------------------------- 151

5.8.5 AC Conductivity Measurements ---------------------------------------- 152

5.8.6 Area Specific Resistance (ASR) ----------------------------------------- 153



5.8.9 Performance Measurements --------------------------------------------- 156

5.8.10 Cost Analysis--------------------------------------------------------------- 158

5.8.11 Conclusions ----------------------------------------------------------------- 159

5.9 Sample No. 11 ---------- La0.1Sr0.9Co0.2Zn0.8O3-δ (LSCZ) -------------------- 160

5.9.1 Introduction ---------------------------------------------------------------- 160

5.9.2 Crystallographic View -------------------------------------------------- 160

5.9.3 Scanning Electron Microscopic (SEM) View ------------------------ 161

5.9.4 Electrical DC Conductivity Measurements --------------------------- 162

5.9.5 Electrical AC Conductivity Measurements --------------------------- 163

5.9.6 Area Specific Resistance (ASR) ----------------------------------------- 164




5.9.10 Cost Analysis--------------------------------------------------------------- 171

5.9.11 Conclusions ---------------------------------------------------------------- 172

5.10 Discussions----------------------------------------------------------------- 173

5.10.1 Fuel Cell Fabrication ---------------------------------------------------- 173

References ------------------------------------------------------------------------------------ 177

Chapter No. 6 179

6 Summary, Conclusions and Recommendations ------------ 180

6.1 Summary ---------------------------------------------------------------------------- 180

6.2 Conclusions ------------------------------------------------------------------------- 181

6.3 Further Recommendations ------------------------------------------------------- 185

XIV

List of Figures

Figure 1.1 a) Schematic Diagram of a Typical Fuel Cell ------------------------- 05

Figure 1.1 b) Working of Hydrogen-Oxygen (H2-O2) Fuel Cell ----------------- 05

Figure 1.2 (a-d) Schematic Diagrams Showing the Working of

Different Fuel Cells ------------------------------------------------------- 10

Figure 1.3 An Overview of the Requirements of Fuel Cell Anode Material ---- 16

Figure 1.4 Stationary and Mobile Systems Based on Fuel Cell Technology --- 21

Figure 1.5 Schematic Diagram of Showing Electrochemistry of SOFC --------22

Figure 3.1 Philips X’Pert X-Ray Diffractometer ----------------------------------- 53

Figure 3.2 Bragg’s Law Patterns for XRD ------------------------------------------ 54

Figure 3.3 Scanning Electron Microscope------------------------------------------- 56

Figure 3.4 Transmission Electron Microscopes ------------------------------------ 57

Figure 3.5 Differentials Scanning Calorimetric Analyzer

(DSC 404 F 3 Pegasus) --------------------------------------------------- 58

Figure 3.6 VERSASTAT2273 Potentiostat(Princeton Applied Research,USA) - 60

Figure 4.1 A Flow Chart for Synthesizing BSCM Cathode ------------------------ 76

Figure 4.2 A Flow Chart for Synthesizing LSCZ Cathode ------------------------- 77

Figure 4.3 A Flow Chart for Synthesizing BSCF Cathode ------------------------ 78

Figure 4.4 A Sample Holder for Fuel Cell Measurements ------------------------ 86

Figure 5.1 XRD Patterns of CNZGC Anode Materials

(Sample Dry-1to 9 Odd Compositions) -------------------------------- 89

Figure 5.2 Experimental Set up for Conductivity and

Performance Measurements ---------------------------------------------- 90

Figure 5.3 DC Conductivities of Dry 1-9 (Odd Compositions) at

Hydrogen Atmosphere --------------------------------------------------- 91

Figure 5.4 DC Conductivities of Dry 1-9 (Odd Compositions) at

Air Atmosphere ---------------------------------------------------------- 92

Figure 5.5 Performance of Dry 1-9 (Odd Compositions) at 550oC. ----------- 93

Figure 5.6 Arrhenius Plot of Dry 1-9 (Odd Compositions) at

Hydrogen Atmosphere --------------------------------------------------- 94

Figure 5.7 Arrhenius Plot and its Corresponding Linear Fit Curves

(Inset) for the Calculation of Activation Energy of Dry-7 ---------- 94

Figure 5.8 XRD Patterns of Composition Dry-7 at

XV

Various Sintering Temperatures----------------------------------------- 96

Figure 5.9 Performance of Dry-7 at 550oC

(Sintered at 700, 800, 900 and 1000oC) ------------------------------- 96

Figure 5.10 XRD Patterns of Different Composition of Al0.1NixZn0.9-x,

(x = 0.1 – 0.5) ------------------------------------------------------------- 99

Figure 5.11 XRD Pattern of Composition A0.10N0.20Z0.70-GDC

Composite Anode --------------------------------------------------------- 100

Figure 5.12 Scanning Electron Microscopic Image of Composite

Al0.1Ni0.3Zn0.6-GDC -------------------------------------------------------- 101

Figure 5.13 DC Conductivities of Al0.1NixZn0.9-x Anode at H2 Atmosphere ------ 102

Figure 5.14 AC Conductivities of Al0.1NixZn0.9-x Anode at H2 Atmosphere------- 102

Figure 5.15 Arrhenius Plots of DC Conductivities of Al0.1NixZn0.9-x at

H2 Atmosphere ---------------------------------------------------------- 104

Figure 5.16 Arrhenius Plots of AC Conductivities of Al0.1NixZn0.8-x at

H2 Atmosphere ----------------------------------------------------------- 104

Figure 5.17 Linear Fit Curve of Sample 44(b) for Activation Energy from

DC conductivity at Hydrogen Atmosphere ---------------------------- 105

Figure 5.18 Linear Fit Curve of Sample 44(b) for Activation Energy from

AC conductivity at Hydrogen Atmosphere ------------------------------ 105

Figure 5.19 AC Electrochemical Impeadance Sepctra at Different Temps. ----- 106

Figure 5.20 Performances of Sample No. 44(a), 44(b), 44(c), 44(d) and 44(e) -- 107

Figure 5.21 XRD Pattern of Cu0.2Mn0.2Zn0.6 Electrode Sintered at 800oC ------- 111

Figure 5.22 SEM Image of Cu0.2Mn0.2Zn0.6 Electrode ------------------------------- 111

Figure 5.23 DC Conductivities of Electrode at H2 and Air Atmosphere ---------- 113

Figure 5.24 Arrhenius Plot of DC Conductivity at Hydrogen Atmosphere ------- 114

Figure 5.25 Arrhenius Plot of DC Conductivity at Air Atmosphere --------------- 114

Figure 5.26 Comparisons of AC Impedance Spectra of Different Ratios of

Electrode to Electrolyte (wt. %age of Electrode to Electrolyte) ---- 116

Figure 5.27 Conductivity of CMZ Electrode Containing Different wt. % of

NSDC Electrolyte Measured at 550oC ---------------------------------- 117

Figure 5.28 Performances of CMZ Electrode Containing Different wt. % of

NSDC Electrolyte Measured at 550oC ---------------------------------- 118

Figure 5.29 Fuel Cell Performance of Electrode Having 80 wt. % CMZ and

XVI

20 wt. % NSDC over a Temperature Range of 400-550oC ---------- 118

Figure 5.30 Crystallographic View of Ba0.05Cu0.25FexZn0.70-xAnode,

Where x = 0, 0.02, 0.04, 0.06, 0.08, 0.10 and 0.12 mol % ----------- 122

Figure 5.31 X-Ray Diffractions Patterns of BCFZ-5, Anode, BSCF Cathode

and NK-CDC Electrolyte Materials ------------------------------------- 123

Figure 5.32 SEM Micrograph of BCFZ-5 Anode Material ------------------------- 123

Figure 5.33 Electrical DC Conductivities of BCFZ (1-6) Materials at

Hydrogen Atmosphere ----------------------------------------------------- 125

Figure 5.34 Electrical DC Conductivities of BCFZ (1-6) Materials at

Air Atmosphere ------------------------------------------------------------- 125

Figure 5.35 Arrhenius Plot of BCFZ-5 from DC Conductivity Data at H2 atm. - 127

Figure 5.36 Arrhenius Plot of BCFZ-5 from DC Conductivity data at Air at. --- 127

Figure 5.37 AC Impedance Spectroscopy of Pure BCFZ-5

AnodeMaterial in Temperature Range (300-600oC) ------------ 128-131

Figure 5.38 AC Electrochemical Impedance Spectroscopy of BCFZ-5 Anode -- 132

Figure 5.39 Symmetrical Fuel Cell Performances of BCFZx at 550oC using

NK-CDC Electrolyte, Where x = 1, 2, 3, 4, 5 and 6 ------------------- 134

Figure 5.40 Performance of BCFZ-5-NKCDC/NKCDC/BSCF-NKCDC

Fuel Cell in Temperature Range of 400-550oC ------------------------ 135

Figure 5.41(a) Short-term Stability for OCV Test of Cell at 550oC------------------- 136

Figure 5.41(b) Short-term Stability for Power Density Test of Cell at 550oC--------136

Figure 5.42 Crystallographic View of Ba0.15Fe0.10Ti0.15Zn0.60(BFTZ)

Anode Material ------------------------------------------------------------- 140

Figure 5.43 Electrical DC and AC Conductivity of BFTZ at

Hydrogen Atmosphere ---------------------------------------------------- 141

Figure 5.44 Arrhenius Plot of BFTZ from DC Conductivity atH2 Atm. ---------142

Figure 5.45 Arrhenius Plot of BFTZ from AC ConductivityatH2 Atmosphere - 142

Figure 5.46 (a) Performance of Fuel Cell having BFTZ Anode,

NK-CDC Electrolyte and BSCF Cathode ------------------------------- 144

Figure 5.46 (b) Performance of Fuel Cell having BFTZ Anode,

Conventional NSDC Electrolyte and BSCF Cathode ----------------- 144

Figure 5.47 XRD Pattern of Ba0.4Sr0.6Co0.3Mn0.7O3-δ (BSCM) Cathode -------- 150

Figure 5.48 Microstructure of BSCM Cathode Material by SEM Analysis ------- 150

Figure 5.49 DC Conductivity of Pure BSCM Cathode at Air and H2 atm. --------151

XVII

Figure 5.50 AC Conductivity of Pure BSCM Cathode at Air and H2 atm. -------- 152

Figure 5.51 Area Specific Resistance of BSCM Cathode at Hydrogen atm. ----- 153

Figure 5.52 Arrhenius Plot of BSCMCathode at Air Atmosphere ---------------- 154

Figure 5.53 Arrhenius Plot of BSCMCathode at Hydrogen Atmosphere -------- 154

Figure 5.54 AC Electrochemical Impedance Spectra of Pure BSCM

Cathode Material --------------------------------------------------------- 155

Figure 5.55 (a) Performance of Fuel Cell using BCFZ-5-NKCDC Anode,

NKCDC Electrolyte and BSCM-NKCDC Cathode ------------------- 156

Figure 5.55 (b) Performance of Fuel Cell using BCFZ-5-NSDC Anode,

NSDC Electrolyte and BSCM-NSDC Cathode ------------------------ 157

Figure 5.55 (c) Performance of Fuel Cell using Ni-NKCDC Anode,

NKCDC Electrolyte and BSCM-NKCDC Cathode -------------------- 157

Figure 5.55 (d) Performance of Fuel Cell using Ni-NSDC Anode,

NSDC Electrolyte and BSCM-NSDC Cathode ------------------------ 158

Figure 5.56 XRD Pattern of La0.1Sr0.9Co0.2Zn0.8O3-δ(LSCZ) Cathode Material - 161

Figure 5.57 Microstructure of LSCZ Cathode by SEM Analysis ------------------- 162

Figure 5.58 DC Conductivity of LSCZ Cathode Material at

Air and H2 Atmosphere ---------------------------------------------------- 163

Figure 5.59 AC Conductivity of LSCZ Cathode Material at

Air and H2 Atmosphere ---------------------------------------------------- 164

Figure 5.60 Area Specific Resistance of LSCZ Cathode Material ----------------- 165

Figure 5.61 Arrhenius Plot from DC conductivity Data at Air Atmosphere ----- 166

Figure 5.62 Arrhenius Plot from DC Conductivity Data at H2 Atmosphere ---- 166

Figure 5.63 AC Electrochemical Impedance Spectroscopy ------------------------- 167

Figure 5.64 (a) Performance of Fuel Cell using BCFZ-5-NKCDC Anode,

NKCDC Electrolyte and LSCZ-NKCDC Cathode ------------------- 169

Figure 5.64 (b) Performance of Fuel Cell using BCFZ-5-NSDC Anode,

NSDC Electrolyte and LSCZ-NSDC Cathode -------------------------- 169

Figure 5.64 (c) Performance of Fuel Cell using Ni-NKCDC Anode,

NKCDC Electrolyte and LSCZ-NKCDC Cathode --------------------- 170

Figure 5.64 (d) Performance of Fuel Cell using Ni-NSDC Anode,

NSDC Electrolyte and LSCZ-NSDC Cathode ------------------------ 170

XVIII

List of Tables

Table 1.1 Comparative Chart of Fuel Cell Technologies ------------------------ 06

Table 1.2 Chemical Reactions Accruing in Fuel Cells --------------------------- 10

Table 1.3 Pros and Cons of Fuel Cells --------------------------------------------- 11

Table 1.4 Research Groups Working on Anode Materials to Promote

Fuel Cell Technology ----------------------------------------------------- 18

Table 4.1 Sample No. 1; Composition Detail of CNZGC (Anode Material) -- 63

Table 4.2 Sample No. 2; Composition Detail of ANZ (Anode Material) ------ 63

Table 4.3 Sample No. 3; Composition Detail of CMZ (Anode Material) ----- 63

Table 4.4 Sample No. 4; Composition Detail of BCFZ (Anode Material) ---- 64

Table 4.5 Sample No. 5; Composition Detail of BFTZ (Anode Material) ---- 64

Table 4.6 Sample No. 6; Composition Detail of NK-CDC

(Electrolyte Material) ----------------------------------------------------- 64

Table 4.7 Sample No. 7; Composition Detail of GDC-Y2O3


Table 4.8 Sample No. 8; Composition Detail of NKSDC


Table 4.9 Sample No.9; Composition Detail of NSDC


Table 4.10 Sample No. 10; Composition Detail of GDC (Electrolyte Material) 65

Table 4.11 Sample No. 11; Composition Detail of BSCM (Cathode Material) - 65

Table 4.12 Sample No. 12; Composition Detail of LSCZ (Cathode Material) -- 65

Table 4.13 Sample No. 13; Composition Detail of BSCF (Cathode Material) -- 65

Table 4.14 Price List of Chemicals from Sigma Aldrich--------------------------- 66

Table 4.15 Work Scheme to Prepare Composite Anode and Cathode Materials 79

Table 4.16 Scheme to Prepare Complete Cell for Performance Measurements- 83-

85

Table 5.1 Crystallite Size Data of each Composition of CNZGC ---------------- 89

Table 5.2 Conductivity, Activation Energy and Performance

Data of CNZGC ------------------------------------------------------------ 93

Table 5.3 Average Particle Size Data of Dry-7 Composition -------------------- 95

Table 5.4 Estimated Cost of Dry-7 Electrode

(Cu0.13Ni0.24Zn0.32Gd0.12Ce0.19) CNZGC----------------------------------- 97

XIX

Table 5.5 Conductivity, Activation Energy and Particle Size Data of ANZ ---- 103

Table 5.6 Performance Data of ZNZ-GDC Composite Anode ------------------ 108

Table 5.7 Estimated Cost of 44(b) Electrode (Al0.10Ni0.20Zn0.70) ANZ----------- 108

Table 5.8 Particle Size, ASR, Conductivity, Activation Energy and

Performance ---------------------------------------------------------------- 115

Table 5.9 Conductivity and Performance of CMZ100-x-NSDCxAnode --------- 119

Table 5.10 Estimated Cost of (Cu0.2Mn0.2Zn0.6) CMZ Electrode------------------ 119

Table 5.11 Particle Size Activation Energy and Electrical Conductivity Data - 126

Table 5.12 Performance of Symmetrical BCFZ (1-6) Fuel Cell ------------------ 135

Table 5.13 Performance of Non-Symmetrical BCFZ-5 Fuel Cell ---------------- 136

Table 5.14 Estimated Cost of BCFZ-5 Electrode (Ba0.05Cu0.25Fe0.10Zn0.60) ----- 137

Table 5.15 Particle Size, Conductivity and Activation Energy of BFTZ Anode - 141

Table 5.16 Performance Data of BFTZ Anode Material --------------------------- 145

Table 5.17 Estimated Cost of BFTZ Electrode (Ba0.15Fe0.10Ti0.15Zn0.60) --------- 145

Table 5.18 Particle Size, ASR, Activation Energy and

Conductivity ofBSCM Cathode ----------------------------------------- 152

Table 5.19 Fuel Cell Performance Data Based on BSCM Cathode Material --- 158

Table 5.20 Estimated Cost of BSCM Cathode (Ba0.40Sr0.60Co0.20Mn0.80) -------- 159

Table 5.21 Particle Size, ASR, Activation Energy, and

Conductivity of LSCZ ----------------------------------------------------- 164

Table 5.22 Fuel Cell Performance Data Based on LSCZ Cathode Material ---- 171

Table 5.23 Estimated Cost of LSCZ Cathode (La0.10Sr0.90Co0.20Zn0.80) ---------- 172

Table 5.24 Comparative Homework of Cost Analysis of Electrode Materials - 175

Table 5.25 Comparative Homework of Cost Analysis of Electrolyte Materials - 175

Table 6.1 Comparative Chart of Performance of BCFZ-5 Anode ------------- 181

Table 6.2 Comparative Chart of Particle Size, Electrical Conductivity and

Activation Energy of All the Samples ------------------------------------ 182

Table 6.3 Fuel Cells Performance Data of All the Fuel Cells ------------------- 183

XX

ABSTRACT

Fuel cell is an emerging, cleanest, environmental friendly and pollution free

technology, which converts chemical energy of fuel into electricity, heat and power

without combustion. Fuel cells are categorized according to their electrolytic

materials and working temperature. Solid oxide fuel cell (SOFC) is the most

dominant and prominent among the fuel cell family. In other words, fuel cell is one

of the most competitive candidates that could provide possibly accomplishments.

Conventionally, Ni-YSZ cermet anode is used in SOFC, which works in the

temperature range of 800-1000oC. Although this anode possesses a high

electrochemical activity, high performance as well as electronic conductivity yet it

requires a high working temperature to achieve the optimal results. Its high working

temperature is the present draw back which becomes a major barrier to its

commercialization. If this cell has to be commercialized then there is need to find

suitable electrode materials that can operate successfully at low operating

temperature. Keeping this in mind, many new electrode materials have been

introduced in the present work, which have been classified into two groups; one is

containing Ni partially while the other is completely Ni free.

New electrode materials were prepared by introducing nano technique using

either dry or wet chemical method with an added advantage of low manufacturing

temperature. In order to fabricate a complete fuel cell, the compatible electrolyte

materials were also prepared by co-precipitation method. These materials exhibited

an excellent performance at comparatively low temperature (400-600oC).

For SOFC electrode and electrolyte purpose, CuNiZnGdCe (CNZGC),

Al0.1NixZn0.9-x (ANZ), Cu0.2Mn0.2Zn0.6 (CMZ), Ba0.05Cu0.25FexZn0.7-x (BCFZ),

XXI

Ba0.15Fe0.10Ti0.15Zn0.60 (BFTZ), Ba0.4Sr0.6Co0.3Mn0.7 (BSCM), La0.1Sr0.9Co0.2Zn0.8

(LSCZ), Na2CO3-K2CO3- Ca0.2Ce0.8 (NK-CDC) and Gd0.1Ce0.9-Y2O3 (Y-GDC)

materials were successfully synthesized by solid state reaction method or wet

chemical and co-precipitation method. These electrodes and electrolyte materials

were characterized by XRD, SEM, TEM, electrochemical and electrical techniques.

It has been found that the BCFZ-5 having a composition of Ba0.05Cu0.25Fe0.10Zn0.60

shows an electrical conductivity equal to 25.84 at hydrogen atmosphere. It also

exhibited the maximum power density of 741.87mW/cm2 and 933.41mW/cm2 for

symmetrical and asymmetrical fuel cell testing schemes. On the basis of these

results, BCFZ-5 material is considered a promising electrode/anode candidate for

low temperature solid oxide fuel cell.

Different approaches have been implemented to reduce the present cost of

electrode and electrolyte materials for solid oxide fuel cell. For example;

I. Use of cheap raw material

II. Lowering of sintering temperature

III. Reduction of sintering time

IV. Lowering of operating/working temperature

It has been noted that the substitution of zinc compound Zn(NO3)2.6H2O in place of

nickel oxide (NiO) has reduced the cost by a factor of ≈25 in addition to the lowering

of manufacturing and operating temperature, which also reduces the cost indirectly by

saving energy and time. Moreover, the cost has been further reduced by a factor of 35

and 18 when samarium nitrate Sm(NO3)3.6H2O and gadolinium nitrate

Gd(NO3)3.6H2O are respectively replaced by calcium nitrate Ca(NO3)2.4H2O.

XXII

The lowering of working temperature from 1000 to 550oC is a major

achievement that would not only reduce the running cost yet it may help in

commercialization of solid oxide fuel cell.

In a nut shell the electrodes and electrolytes proposed in the present work

have successfully lowered the manufacturing as well as working temperature and

hence the operational cost along with a significant reduction in the manufacturing

cost of solid oxide fuel cell (SOFC).

Key words: Solid Oxide Fuel Cell (SOFC), Zn Based Electrodes, Nano-composites

Electrodes, Energy Conversion Device, Ceria Carbonated Fuel Cell, Advanced Fuel

Cell, Efficient Device, BCFZ anode, NKCDC electrolyte, Novel Cathode

Chapter No. 1

Chapter No. 1 Introduction

2

1 INTRODUCTION

1.1 Importance

The consciousness of the entire world is increasing to find out alternative

energy sources due to rapidly depleting fossil fuels (coal, oil, natural gas, etc.). At

present, these fossil fuels can provide more than 90% of the world’s energy demand

[1]. Ultimately, these resources will be exhausted. It is therefore important to find out

some alternate such as renewable energy sources. These sources could be utilized to

create energy and power for different purposes. The scientists, engineers and

researchers are trying to find out alternate energy sources since long.

1.2 Non-Renewable Energy Sources

Fossil fuels are formed from the compression of dead plants and animal life

that remain buried in the earth over millions of years. These fuels fall under the

category of non-renewable sources of energy because the deposits cannot be

replenished [1]. Fossil fuels burn to release chemical energy, which was stored

within the resource. Although fossil fuels have been around long before the

discovery of fire yet our forefathers had no use for them. In the late 1800’s, use of

coal and gas was started in steam locomotives.

1.3 Renewable Energy Sources

Renewable energy is that energy which never comes to an end and can be

replenished in short intervals of time. The water, solar, wind, geothermal and biomass

is the main renewable energy sources.

1.3.1 Water

Water is a precious and a kind present of ALLAH. Water is categorized in

renewable energy source because water is obtained from rain and melting ice. It can


3

be stored in dames where from its potential energy can be utilized for producing

electricity.

1.3.2 Solar

The sun is a huge energy source for billions of years. Sun’s radiations that

reach the earth are called solar energy which consists of heat and light. Solar ovens,

solar cells and solar panels are utilized in term of solar energy for their working. This

energy can also be used for the desalination of brackish water, dehydration of fruits.

The earth is made of very different types of land which absorb sun’s heat at different

rates [2]. Electricity van be generated by solar energy; e. g. solar cells devices are

used to convert the solar energy into direct electricity.

1.3.3 Wind

Naturally occurring wind energy is being directly used in the form of

windmills to generate electricity. Batteries are charged with this energy or pump can

be run underground water. Electricity is produced by large modern wind turbines and

these turbines are operated in ‘wind farms’.Localized energy needs can be fulfilled

easily by constructing small wind turbines.

1.3.4 Geothermal

Geothermal energy has been known since long time as evidenced by the

presence of “hot springs” flow of magma during volcanic eruption. Deep mining and

drilling into the earth during oil and gas exploration has also been manifesting the

presence of heat in the earth core. The temperature increases gradually while going

deep into the earth. The rate at which temperature of earth increases with depth is

called thermal gradients and is expressed as degree per kilometer. Its average value is

25oC/km. This means some heat is always coming out of earth and could be used for

useful purpose. The energy obtained from earth in this manner is called geothermal


4

energy. The heat present inside the earth can produce steam and hot water which may

be employed to heat buildings or for generating electricity. Geothermal energy falls

under the category of renewable energy. Because, underground water is restored by

rainfall and heat always presents inside the earth so geothermal energy is a renewable

energy source [2].

1.3.5 Biomass

Organic materials evolved from plants and animals are called biomass. Fuel

wood derived from the trees is the largest source of bio mass energy. It contains

stored energy from the sun, which can be transformed into other sorts of energy for

many applications. Wood, crops, garbage, landfill gas and alcohol are different types

of the biomass, which supply energy for appropriate applications [3].

1.3.6 Alternative Energy Sources

Fuel cell is another source which can work as renewable energy source. Its

idea was floated by Sir Willium Robert Grove (1811-1896) who proposed that if

passage of electric current through water could yield hydrogen and oxygen then the

reverse process must yield electricity. Fortunately, he was able to develop a device

that produces electricity on combining hydrogen and oxygen. He named it as “gas

battery” which latter on was called “fuel cell” by Ludving Mond and Charles Langer

in 1889[4].

1.4 Fuel Cells

Fuel cells are electrochemical devices that change energy of hydrogen directly

into electricity, heat and water as by-product. Fuel cells are swiftly rising energy

exchange technology contributing elevated efficiencies and significantly lower release

than that of conventional technologies. Principally, a fuel cell is composed by


5

consecutive three layers of anode/electrolyte/cathode. Electrolyte is sandwiched by

anode and cathode. Generally, electrodes are responsible to dispense hydrogen (as

fuel) into ions and contain channels to transfer electrons or negative ions through an

external circuit [5].

Fuel cell is like a “factory” that takes fuel (hydrogen) as input and provides

electricity as output. A fuel cell will carry onto churn out electricity as the time that

fuel is supplied. Figure 1.1(a) exhibits a general concept of working of hydrogen-

oxygen (H2-O2) fuel cell. When hydrogen gas is supplied at its anode, it splits up into

protons and electrons due to existence of a catalyst. When these electrons pass

through an external circuit, they constitute an electric current as exposed in Figure

1.1(b).

Figure 1.1: a) Schematic Diagram of a Typical Fuel Cell

b) Working of Hydrogen-Oxygen (H2-O2) Fuel Cell

1.4.1 Types of Fuel Cells

Fuel cells are classified into several types. Each type possesses its own advantages,

limitations and potential applications. These Fuel cells are categorized primarily by

the variety of electrolyte they employ and the chemical reactions that take place in the

cells and secondly their working temperature. The applications for which these fuel

cells are most suitable are influenced on the dependence of its electrolyte. A list of


6

major types of fuel cells is given in Table 1.1 along with their schematic diagrams in

Figure 1.2(a-d). A brief explanation of each type follows Table 1.1.

Table 1.1: Comparative Chart of Fuel Cell Technologies

Fuel Cell Type

Electrolyte Working Temp.

System Output

Electrical Efficiency

Applications

Alkaline Fuel Cell (AFC)

Aqueous solution of KOH in a matrix

90-100oC 10kW-100kW

60% Military space

Phosphoric Acid Fuel Cell (PAFC)

Liquid phosphoric acid soaked in a matrix

150-200oC 50kW-1MW > 40% Distributed generation

Molten Carbonate Fuel Cell (MCFC)

Liquid solution of lithium, sodium and/or potassium carbonates soaked in a matrix

600-700oC <1kW-1MW 45-47% Electric utility Large distribution generation

Proton Exchange Membrane Fuel Cell (PEMFC)

Solid organic polymer polyflurosulfonic acid or Nafion/Teflon ®

50-100oC <1kW-250kW

53-58% (transportation) 25-30% (stationary)

Backup power Portable power Transportation Small distributed generation

Solid Oxide Fuel Cell (SOFC)

Yttria Stabilized Zirconia (YSZ) and doped ceria

400-1000oC

<1kW-3MW 35-43% Auxillary power Electric utility Large distribution generation

1.4.1.1 Alkaline Fuel Cells (AFCs)

Aqueous solution of potassium hydroxide (KOH) in a matrix is used as the

electrolyte in AFCs. A variety of non-precious metals like stainless steel are used as

catalysts at electrodes. These fuel cells operate at temperature ranging between 65oC

to 250oC. The hydroxyl ion (OH-) is the charge carrier for AFC that transfer from

cathode to anode to react with hydrogen to produce water and electron. The water

thus produced goes back to cathode and regenerates hydroxyl ions [6].

Newly developed AFCs designs operate at approximately 75°C. They have

been tested to drive road automobile for passenger and cargo [6]. AFCs also have


7

been widely used in spacecraft and submarines. These fuel cells are being used by

National Aeronautics and Space Administration (NASA). About 70% electrical power

can be obtained on board by these fuel cells as well as drinking water. The poisoning

by carbon monoxide (CO2) is the disadvantage of this fuel cell.

1.4.1.2 Phosphoric Acid Fuel Cells (PAFCs)

An electrolyte material of phosphoric acid fuel cell PAFC is made by a liquid

phosphoric acid. The electrolytic acid is enclosed in a Teflon-bonded matrix. Porous

carbon electrodes hold platinum catalyst. The efficiency of these fuel cells for the

production of electricity is approximately 40% and operating temperature is 200°C.

PAFCs are fit for commercial or small industrial applications. The systems with a

production capacity of 200kW are currently available. Pilot plants capable of

generating 1.3MW and 11 MW have been built in Italy and Japan, respectively, but

they are still expensive (2,500 EURO/kW) [7]. At the anode side, hydrogen is

distributed into protons and electrons. The protons (H+) pass through the electrolyte

and reach at cathode, where it combines with the air/oxygen to produce water. The

electrons transfer through an external circuit in order to perform useful work. This

type of reaction also produces heat as a by product in fuel cell [6]. It may be noted

that water produces at cathode unlike AFCs as shown in Figure 1.2(b).

1.4.1.3 Molten Carbonate Fuel Cells (MCFCs)

A molten carbonate mixture hanging in a porous, chemically inert ceramic

lithium aluminum oxide (LiAlO2) matrix is used as electrolyte material in MCFCs. Its

working is quite different with respect to other fuel cells. The electrolyte used in this

fuel cell consists of two salts in molten form; lithium carbonate and sodium carbonate

or lithium carbonate and potassium carbonate. In order to achieve high mobility

through electrolyte, it is necessary to provide high temperature to melt carbonate.


8

Therefore, MCFCs fall under the category of high temperature fuel cells [6]. When

650oC temperature is provided, these melted carbonates become conductive and

carbonate ions (CO32-) flow from cathode to anode where they combine with

hydrogen to produce water, carbon dioxide and electrons. These electrons flow

through an external circuit and go back to cathode generating electricity, and heat as a

byproduct. The net electricity efficiency of these fuel cells is approximately 55%.

MCFCs are operated at 650°C which are suitable for industrials and utilities

applications. Who’s operating temperature lies between 200°C and 600°C.Corrosion,

durability and reliability are still technical problems need address to be solved.

1.4.1.4 Proton Exchange Membrane Fuel Cells (PEMFCs)

These fuel cells contain a solid polymer as electrolyte material. PEMFC are

also called Polymer Electrolyte Fuel Cell (PEFCs) or Solid Polymer Fuel Cells

(SPFC). These fuel cells are operated in a temperature range of 60-130°C.

Transportation, portable and cogeneration in building are the major applications of

PEMFC. Power generation is also an application of and with an additional advantage

to avoid grid-reinforcement [8].

Low temperature operation rakes less time to warm up which toleratesfuel cells to

establish function quickly. Lowering temperature exhibits the better durability than

high temperature fuel cells. For these fuel cells, platinum (a noble metal catalyst) is

used as electrode material, which separates hydrogen into electrons and protons

supplied at anode. However, it is extremely sensitive to carbon monoxide (CO)

poisoning that reduces the reaction rate at the anode. The concentration of CO is

observed to be in the order of 0.5-5 %, depending on the temperature and the

concentration of other gases. Since, CO forms a layer to complete a monolayer on the

platinum (Pt) or Pt-alloy catalyst whose operating temperature is less than 100oC [7].


9

In early PEMFC a huge quantity of platinum was used as a catalyst for electrode

materials. Therefore, Proton exchange membrane fuel cells could not be

commercialized due to high cost of Platinum (Pt). In order to overcome this bottle

neck reconfiguration of PEMFC using low cost materials is highly required to make

these cells commercially viable [9].

In construction of PEM Fuel Cells, hydrogen is very important substance which

produces e-, H+ and water as a result of chemical reaction that is held at anode side.

The chemical reactions can be illustratedin Table 1.2[8].

1.4.1.5 Solid Oxide Fuel Cells (SOFCs)

In solid oxide fuel cells, electrolyte is consisted of an inflexible, non-porous

compound of ceramic materials. The performance of solid oxide fuel cells (SOFCs) is

comparable to that of molten carbonate fuel cells (MCFCs) and can be used for all

those purposes where an MCFC can be used. Its operating temperature is between

700°C and 1000°C. A power plant, based on SOFCs having a power of 100 kW is

operating in Holland. The central part of the SOFC is called electrolyte. The role of

solid oxide material which works as an electrolyte is very important in this kind of

fuel cell, because the competence of the cell is directly linked with the ionic

conductivity of the electrolyte [10].

Oxygen ions (O2-) are the charge carriers in solid oxide fuel cells. The oxygen

molecules come apart into four numbers of electrons and oxygen ions at the cathode

side, when air or oxygen is used as oxidant. These oxygen ions surpass through

electrolyte material and merge with hydrogen at the anode side by discharging four

electrons. These electrons move through an external circuit to produce electricity [6].


10

Figure 1.2: Schematic Diagrams Showing the Working of Different Fuel Cells [11]

a) Alkali Fuel Cell b) Phosphoric Acid & PEM Fuel Cell c) Molten Carbonate Fuel Cell d) Solid Oxide Fuel Cell

Table 1.2: Chemical Reactions Accruing in Fuel Cells

Fuel Cell

Type

Anode Reaction Cathode Reaction Overall Reaction

AFC 2H2 + 4OH- => 4H2O + 4e- O2 + 2H2O + 4e- => 4OH- 2H2+ O2 => 2H2O

PAFC 2H2 => 4H+ + 4e- O2(g) + 4H+ + 4e=> 2H2O 2H2 + O2 => 2H2O

MCFC CO32-

+ H2 => H2O + CO2 + 2e- CO2 + 1/2O2 + 2e => CO3

2- H2(g) + 1/2O2(g) + CO

(cathode) =>

H2O(g) + CO2 (anode)

PEMFC H2 => 2H+ + 2e

- ½O2 + 2H

+ + 2e=> H2O 2H2+O2 => 2H2O

SOFC 2H2 + 2O2- => 2H2O+ + 4e- O2+ 4e- => 2O2- 2H2 + O2 => 2H2O

CO –carbon monoxide e- -electron H2O –water CO2 –carbon dioxide H+ -hydrogen ion O2 –oxygen CO3 -carbonate ion H2 -hydrogen OH- -hydroxyl ion


11

Table 1.3: Pros and Cons of Fuel Cells

Fuel Cell Types Pros Cons

Alkaline Fuel Cell (AFC)

♣Improved cathode performance ♣Potential for non-precious

metal catalysts ♣Low cost of materials

♣Must use pure H2-O2 gases ♣Potassium hydroxide KOH electrolyte may need occasional replenishment ♣It needs compulsory removal of water from its anode

Phosphoric Acid Fuel Cell (PAFC)

♣Mature technology ♣Excellent reliability and

long termperformance ♣Electrolyte is relatively low

cost

♣Pricey platinum catalyst ♣Easily affected by CO and sulphur poisoning ♣Liquid electrolyte destroy

gradually must be replaced occasionally

Molten Carbonate Fuel Cell (MCFC)

♣Fuel flexibility ♣Non precious catalyst ♣High quality waste heat for

cogenerationapplication

♣Must implement CO2 recycling ♣Easily affected, molten electrolyte ♣Degradation and life time issues ♣Relatively costly materials

Proton Exchange Membrane Fuel Cell (PEMFC)

♣Its power density is highest amongst all thefuel cell classes ♣Good start-stop capabilities ♣Low-temperature operation

makes it suitable for portable applications

♣Use of expensive platinum catalyst ♣Polymer membrane and auxiliary components are expensive ♣Very poor CO and S tolerance

Solid Oxide Fuel Cell (SOFC)

♣Fuel flexibility, hydrogen and carbondioxide can be used as fuel in SOFC. ♣Non precious metal

catalysts ♣Solid electrolyte

♣Significant high temperature materials issues ♣High temperature is barrier to

tolerate relatively impure fuels ♣Expensive components/fabrication

Almost all the fuel cells such as PEMFC, MCFC, PAFC and AFC make use of

a single fuel such as hydrogen, whereas an SOFC has an advantage of using a variety

of fuels such as fossil fuels, gaseous fuels, methane, ethane, propane, butane and

pentane etc. Carbon dioxide (CO2), nitrogen, helium and hydrogen sulfide can also be

used as a fuel. Moreover, all the other fuel cells get poisoned by carbon monoxide

(CO) [12] but SOFC can use CO as a fuel. These cells cannot be poisoned by carbon

monoxide (CO). These types of cells can work as Polyegeneration system. The

efficiency of SOFC is more than 60% which is higher than other fuel cells. The ability

of SOFC to use fossil fuels makes it a dominant technology in comparison to the


12

technologies using other fuel cells. This means SOFC can utilize existing network of

fossil fuels while the other fuel cells require an arrangement of hydrogen gas station.

To make SOFCs more viable its cost has to be reduced to an acceptable level. This

can be achieved through developing materials with improved electrochemical

properties.

1.5 How SOFC Works

Solid oxide fuel cell (SOFC) is considered as one of the best promising power-

creation technology for future applications because it has many advantages over other

fuel cells; like efficient and clean conversion of chemical energy to electricity,

pollution free, no need for water management [13]. However, SOFCs have to face

numerous challenges for commercialization due to their elevated operating

temperature in the range of 800-1000oC. In order to mature commercially viable

SOFCs, considerable research works are being equipped with the aim to decrease cell

operating temperature as low as 400-600oC [14]. The performance of the SOFCs

typically decreases as the temperature is reduced, mainly contributed by electrolyte’s

ohmic resistance and the cathode’s polarization resistance. Novel and high

performance electrolytes and electrodes must be developed for the low temperature

SOFCs. Ionic conductivity of electrolyte of 0.1 Scm-1 is the requirement for the best

solid oxide fuel cells (SOFCs) [14].

A lot of research is in progress for developing suitable nano-material which may

enhance the efficiency of fuel cells. For this reason, different nano-structured ceramic

materials are frequently being used in SOFC. Now researchers have started to use

nano sized particle in the fabrication of SOFC materials [15]. Nano sized electrolyte

materials like Yttria Stabilized Zirconia (YSZ), Gadolinium Doped Ceria (GDC and

Samarium Doped Ceria (SDC) powder permits a reduction of the temperature during


13

the cell fabrication process [15]. For example, nano-crystalline Ceria (Ce) is a proton

conducting composite material which has mixed electronic –ionic conduction

properties, and it is used to promote the charge transport phenomenon at the interface

of electrode –electrolyte [15]. Yttrium Stabilized Zirconium (YSZ) electrolyte

material has been widely used in traditional high temperature SOFCs. However, the

use of YSZ requires operation temperature as high as 1000oC, which limits its choice

as a component material in SOFC [16]. Ceria doped with gadolinium and Samarium

and, bismuth oxide doped with yttrium and erbium oxide are promising electrolytes

since they exhibit much higher ionic conductivity at comparatively low temperature

as that of YSZ at 1000 oC[10]. These dopants have been shown to produce the highest

conductivities in ceria (approximately 0.1 Scm-1 at 700oC and 10-2 Scm-1 at 500oC)

[16]. Widespread improvement has been developed in the study of low-temperature

SOFCs based on doped ceria oxide thin-film electrolyte [10, 15]. However, the

electronic conduction has been introduced by the reduction of Ce4+ to Ce3+, which

causes a loss in power density of solid oxide fuel cell [17]. In order to attain

considerable fuel cell output, the electrolyte material should be fabricated into a dense

ceramic as thin as 10µm to. However, numerous difficulties related to fabricating thin

film are to be addressed, which can cause barriers to promote practical fuel cells for

marketable applications. In present decades, various ceria-salt composites have been

investigated for intermediate temperature SOFCs as electrolyte material by several

researchers [18]. Ion doped ceria is a major candidate for these materials, gadolinium

doped ceria (GdxCe1−xO2), GDC, samarium doped ceria (SmxCe1−xO2), SDC or

yttrium doped ceria (YxCe1−xO2), YDC, are the good examples of new ceria oxide

electrolytes for solid oxide fuel cell. Other salts or compounds are also concerned

with oxalic acid salts, halides, carbonates and hydroxides. In composite electrolytes,


14

electronic conduction is suppressed in reducing atmosphere and conductivity is

enhanced compared to pure DCO, at low temperature. Hence, the volatilization of the

salt becomes a barrier to the long-time application. It is also a key issue to use

electrolyte materials with good performance to develop low temperature SOFCs. Vast

area of interface and larger grain boundaries have been significantly found in nano-

structured materials. Nano-structured enlarges density of transportable defects in the

space charge region [15-17].

It has also been reported that indigenous characteristics are changed in terms of

ionic and electronic charge carrier’s transport when size of particle is one fourth of the

Debye length [15-18].

1.6 Construction of Solid Oxide Fuel Cell (SOFC)

An electrolyte is sandwiched between electrodes and anode, electrolyte and

cathode are the components of conventional solid oxide fuel cell. All the parts have

their own characteristics and specialty. The solid oxide fuel cells are categorized

according to their working temperature as following;

The solid oxide fuel cells, which work in the temperature range 800-1000oC

using YSZ electrolyte, are called conventional solid oxide fuel cells [19].

The solid oxide fuel cells having working temperature in the range of 600-800

oC are called intermediate temperature solid oxide fuel cells. e.g. SDC and

GDC, where SDC stands for samarium doped ceria and GDC for gadolinium

doped ceria electrolytes based solid oxide fuel cells are intermediate fuel cells

[20-21].

Low temperature solid oxide fuel cells work in the temperature range 400-

600oC using two phase electrolyte (carbonate coated ceria based); e.g. NSDC,


15

NGDC, NKCDC where, N and K represent sodium and potassium carbonates

[18, 22-24].

Three components of solid oxide fuel cell (anode, electrolyte and cathode) are

given below:

1.6.1 Anode

Fuel (hydrogen) is supplied at anode part of solid oxide fuel cell where hydrogen

is spread over the active are of cell’s anode and then distributed into ions and

electrons. The electrons take a trip through an external circuit and grant electronic

current.

Anode component can be classified into two classes during manufacturing.

1) Composite anode 2) Nanocomposite anode

1.6.1.1 Composite Anode

The composite anodes possess both conductivities electronic as well ionic

conductivity to transport ions and to provide a route to electrons. In composite anode,

the precursor raw material of electrolyte is mixed with the precursor material of anode

during manufacturing. The power density and current of a solid oxide fuel cell can

thus be enhanced by combining powders of anode and a ceria based electrolyte with

second phase [26] such as BCFZ (anode); CDC (electrolyte) with NK (2nd phase).

1.6.1.2 Nanocomposite Anode

Nano-technology and nanocomposite approach was adopted by Zhu et al [27-

31]for the improvements of conduction phenomenon of the materials used in solid

oxide fuel cells. They have experimentally proved that nanocomposite materials

exhibit super electronic/ionic conduction at very low temperatures (300-600oC) [32-

35]. It is expected that many technical and economical issues could be solved by

introducing new nanocomposite anode materials. Electrode materials are the


16

fundamental support that contributes to the transfer of electrons; electrolyte

compatibility is another requirement to obtain high performance [36-38].

In order to understand the working and performance of a solid oxide fuel cell,

information arerequired with respect to following: [25].

iii) Catalytic activity ii) Conductivity iii) Open Circuit Voltage (OCV)

iv) Compatibility v) Porosity vi) Stability

Figure 1.3: An Overview of the Requirements of Fuel Cell Anode Material

1.6.1.2.1 Catalytic Activity

Provision of fuel (hydrogen) at anode side of the cell enables cell to perform. The

anode’s function is to distribute fuel into ions (protons and electrons). Therefore, an

anode should be highly catalytically active for the oxidation of the fuel.

1.6.1.2.2 Conductivity

According to Nano-composites for Advanced Fuel Cell Technology NANOCOFC

approach [18], the electrical conductivity should be 10 times equal or greater than

ionic conductivity of the compatible electrolyte used in the cell. Mathematically,


17

1.6.1.2.3 Open Circuit Voltage (OCV)

An anode material must be carrying an open circuit voltage about 1 volt.

1.6.1.2.4 Compatibility

The anode should be chemically, thermally and mechanically compatible to other

components of the fuel cell like electrolyte and cathode. It is a major factor for the

improvement of solid oxide fuel cell. If all the components are compatible to each

other, then maximum power density can be achieved.

1.6.1.2.5 Porosity

An anode should be highly porous for the transportation of ions; this also

increases the mechanical strength of the fuel cell.

1.6.1.2.6 Stability

At certain operating temperature, an anode has to be chemically, physically and

morphologically stable in the fuel (hydrogen gas) environment. It must also be not

affected by the other contaminants.

Numerous works has been done by scientists/researchers to study Ni oxide anode

materials. A ceria carbonate composite is a highly ionic conducting electrolyte which

yields excellent performance of the solid oxide fuel cell in the presence of compatible

electrode. Compatible electrodes play a vital rolefor the development of a high

efficient LTSOFC. In order to use SOFC practically in the future, it is a great

challenge to screen and develop novel electrode materials with minimum area specific

resistance (ASR) [39-40]. In order to fulfill these requirements properly, many

scientist and researchers are developing new electrode materials. The research groups

are illustrated in a Table 1.4 with their names, main interests along with their

published work.


18

Table 1.4:Research Groups Working on Anode Materials to Promote Fuel Cell Technology

Research Groups

Main Researchers

Material Interests References

KTH, Sweden Zhu, B and Raza R Ni-Zn NSDC To improve power density of the cell at low temperature (400-550oC)

[13-14,, 22-24,26-27]

Riso National Laboratory, DK

Mogensen, M and Priimdahl, S

Ni-YSZ, GDC

kinetics,microstructure/performance relation, alternative materials

[41-49]

University of 20 Enschede, NL

De, B. Boer, H.J.M.

Ni, Ni-YSZ Bouwmeester model anodes, kinetics [50-51]

SINTEF/NTNU Trondheim, NO

Aaberg, R. J. and Sunde, S.

Ni, Pt, Ni-YSZ

Microstructure/electrochemistry model anodes, Monte Carlo Simulations

[52-56]

Imperial College, London, UK

Steele, B. C. H., Middleton, P. H.

Nb-ceria, Chromite

Alternative Materials [57-59]

University of St. Andrews, UK

Irvine, J. T. S. Ti-YSZ, Nb, TiO2

Alternative Materials [60-63]

Keele University, UK

Finnerty, C. M., Cunningham,.H., Ormerod, R. M.

Ni-YSZ Catalysis, fuel reforming [64-65]

Research Center, Jülich, D

Holtappels, P et. Al

Ni-YSZ Structural properties, kinetics, degradation, gas transport

[66-83]

University of Karlsruhe, DK

Müller, A., Schichlein, H., Ivers-Tiffe, E.,

Ni, Ni-YSZ Simulations (system indentification), multilayer anode

[84-86]

ETHZ, Zürich, CH

Ekanayake, P., Bieberle, A., Gauckler, L. J.

Ni, Ni-YSZ Microstructure, Kinetics, Model Anode, stste-space modeling

[87-89]

EPFL, Lausanne, CH

Van Herle, J. McEvoy, A. J.

Ni, SZ, Ceria, Chromite

Catalysis, alternative materials [92-93]

University of Genova, I

Kawada, T., Dokiya, M.

Ni-YSZ, Ceria

Partial oxidation, electrochemical reactor, active anode thickness

[94-95]

Tsukuba Research Center,J

Mizusaki, J., Tagawa, H

Ni, YSZ Electrochemical Characterization [96-99]

Yokohama National University, Japan

Uchida, H., Watanabe, M.

Ni, Ni-YSZ Kinetics, model anodes, H2-H2O and CH4-H2O systems

[100-107]

Yamanashi University, Kofu, Japan

Uchida, H., watanabe, M

Pt, Ru Microstructure, catalysis, internal reforming SDC, Ni-YSZ,

[108-114]

Gunma University, Japan

Nakagawa, N., Kato, K.

Ni, Ni-YSZ Triple phase boundary, kinetics [115-117]

Kyushu University, Japan

Eguchi, K. Arai, H.

Ni-YSZ, Ni/ Pt-SDC

Electrochemical characterization, interface analysis

[118-122]

Japan Fine Ceramics Center, Nagoya, Japan

Ohara, S., Mukai, K., Fukui, T.

Ni-YSZ, Ni-SDC

High performance, long term stab [123-126]

Tokyo University, Japan

Abudula, A., Yamada, K

Ni-YSZ Kinetics, reforming [127-131]

Northwestern University, Illinois, USA

Tsai, T., Barnett, S. A.

Ni-YSZ, Ceria

Low temperature, reforming, interfacial Layers

[132-134]

University of Pennsylvania, USA SDC,

Park, S., Gorte, R. J., Worrel, W. L.

Rh, SDC Processing, direct oxidation [135-137]

CSIRO, Victoria, AU

Jiang, S. P., Badwahl, S. P. S

Ni, Pt, Ni-YSZ

Kinetics, p(H2O), model anode [138-140]


19

1.6.2 Electrolyte

The central part of the fuel cell is called electrolyte. Once, the oxygen molecules

have been converted to oxygen ions. These converted oxygen ions must migrate

through this central part of the solid oxide fuel cell towards anode side. The function

of an oxygen ion conductor (O2-) electrolyte is to obstruct the electrons inside the cell

and permit the ions to pass. Therefore, the electrolyte must be a pure high ionic

conductor and not an electronic conductor, i.e. the electronic conductivity of the

electrolyte should approach to zero. It should be compatible to anode as well as

cathode material with all aspects like chemically, thermally and structurally over a

wide temperature range. An electrolyte that can display good performance should

have the following characteristics;

High ionic conductivity at least 0.1S/cm

Minimum electronic conductivity

Low permeability to reactant gases

Stability and compatibility in reducing and oxidizing atmosphere at

temperature less than 1000oC

1.6.3 Cathode

The cathode part of the solid oxide fuel cell is very important part and has a

status of wheel in a vehicle. The cathode material must meet all the anodic material

requirements and be porous to allocate the oxygen molecules to arrive at the

cathode/electrolyte interface. The cathode contributes over 90% of the cell’s

performance as well as provides the structural support to the cell.

1.7 Hydrogen as Fuel

Hydrogen can be prepared through various routs such as:

• Steam on heated carbon.


20

• Decomposition of certain hydrocarbons with heat.

• Reaction of sodium or potassium hydroxide on aluminum.

• Electrolysis of water.

• Displacements from acids by certain metals.

Hydrogen is more safe fuel as compared to gasoline or propane because it is the

lightest element. As soon as hydrogen is released from a container, it immediately

rises upwards and is lost in the environment. For this reason a gas welding torch will

not work until a flame is brought very close to its outlet point. Hydrogen is

abundantly available in our surrounding. This element is also found in stars.

Hydrogen based fuel cell vehicles have a bright future because they have pollution

free transportation. This will also reduce our dependence on fossil fuels [4].

1.8 Fuel Cell Applications

There are many applications of fuel cell technology.The development or

manufacturing of each type of fuel cell makes it attractive for different application;

such as stationary, mobile and portable. The high temperature with high efficiency of

solid oxide fuel cells is a justification of its stationary applications not portable. The

waste of heat can be utilized in the form of heating water, air or cooling.

Conversely, PEMFCs or PAFCs are used for mobile applications due to their lower

operating temperature.

The three principle applications for fuel cells include; [141].

1) Stationary 2) Mobile 3) Portable

1.8.1 Fuel Cells for Stationary Applications

Fuel cells devices can potentially generate electricity for houses/homes,

commerce, establishment and trade with the installation of stationary power plants.

Size of the plants ranges from 1 kilowatt (average home uses 1-5 kW) to numerous


21

megawatts (enough to power institutions or factories). Solid oxide fuel cells are one of

the promise technology which can be used for stationary power distribution because it

can be operated on low cost Zn based electrode.

1.8.2 Fuel Cells for Mobile Applications

The replacement of internal combustion engine into fuel cell based engine

(without combustion engine) is another key commercial application of fuel cells

technology. Now a day, automakers are trying to commercialize a fuel cell car.

Polymer electrolyte fuel cell is the considered a pioneer contestant for

transportationapplications in fuel cell technology. The barrier is still to provide pure

hydrogen fuel.

Solid oxide fuel cells have also many uses. SOFC community is trying to use it

for power and heat generation in electrical systems of vehicles,such as cars, buses and

boats. SOFC can also be linked with a gas turbine to generate electricity[142].

Figure 1.4 Stationary and Mobile Systems Based on Fuel Cell Technology [143]

1.8.3 Fuel Cells for Portable Applications

The energy density requirement is increasing for portable powers sources.

Many technology companies are trying to find an alternate way to enhance the run

time of mobile devices such as cellular phone, laptops, computers, MP3 players and

other electronic devices. Direct Methanol Fuel Cell (DMFC) is an area of intense


22

research and development, which can be utilized for portable applications due to its

low working temperature in the range of 40-60oC.

1.9 Electrochemistry of Solid Oxide Fuel Cell

Figure 1.5 shows the functional set up of a solid oxide fuel cell (SOFC) where

hydrogen is supplied at anode side as a fuel and for an oxidant; air is used at cathode

side. At cathode side, oxygen ions are formed due to reduction of oxidant, and exceed

from beginning to end the electrolyte (e.g. NK-CDC). The driving force has little

partial pressure at anode side. Therefore, the oxygen ions are gist from the electrolyte

toward anode, where hydrogen (fuel) is oxidized. At the anode side, oxygen and

hydrogen are reassembled and response to produce electrons and water on

recombining the hydrogen and oxygen atoms. These produced electrons travel

through an external circuit where they produce electricity.

Figure 1.5: Schematic Diagram Showing Electrochemistry of SOFC


23

1.10 Interest in Study

There is an increasing interest in the area of solid oxide fuel cell because it

possesses high efficiency as compared to other fuel cell family. Fuel flexibility is also

an additional advantageous which makes it able to use widely in this new millennium

for power-generation devices [144].

In the present research work, the main attention was focused in search of low cost

electrode/electrolyte material for Solid Oxide Fuel Cell (SOFC), because it offers

maximum power density. Buthigh manufacturing as well as working temperature

(1600oC and 1000oC, respectively) and high cost are still bottlenecks for its

commercialization. An interest has been employed in prospective development of

solid oxide fuel cell as zero discharge power sources for transportation applications

and unique and extraordinary performance electrodes and electrolytes must be

developed for the low temperature SOFCs [145].

The reduction of present cost of existed materials of solid oxide fuel cell is an

important need to commercialize the solid oxide fuel cell. For this purpose, following

points could be worth considering:

To enhance the reaction sites in the anodic layer, this catalytic layer executes

indirect get in touch with the membrane and the gas diffusion layer to prepare

a structure of membrane electrode assembly (MEA) [146]

To reduce its manufacturing as well as operating temperature

To prevent the anode material to oxidize with the passage of fuel

To increase the electronic conductivity of the electrode material

The developed electrode materials should be porous to oxidize the fuel

The nano-structured electrodes may be developed and studied


24

1.11 OBJECTIVES

The research will be focused on the technologies to compete with

conventional energy conversion systems keeping cost effective and availability

aspects. This methodology provides a solid structure to promote fuel cell

technology and provide a straight framework for the fuel cell related content and

priorities of the straightcurriculum and framework for Research and Development.

Significant research and development activities have been focused to develop

new materials for building of low cost electrodes, which can work at low

temperature in the range 400-600oC.

To reduce its cost for overcoming the energy crises particularly in Pakistan.

To develop and study appropriate electrode materials that may give high

electronic conductivity at low temperature.

To develop and study appropriate electrolyte materials that may give high

ionic conductivity at low temperature.

It is well known that many SOFCs work on the base of Ni-cermet anode

material. The SOFC having this anode with YSZ electrolyte yields good performance.

However, SOFC is still not commercialized, because there are many draw backs of

Ni-cermet anode; i) oxidizing of anode with the passage of fuel ii) deposition of

carbon or sulpher layer when hydrocarbon fuel is used instead of pure hydrogen iii)

fuel cell life problem iv) interfacial resistance v) high manufacturing as well as

working temperature and vi) high cost.

This means the replacement of Ni-cermet anode and drop of the working

temperature of solid oxide fuel cell as well as reduction of manufacturing temperature

of the materials used in solid oxide fuel cell are two major challenges that needs to be


25

addressed by researchers and scientists. The present challenge has been successfully

addressed and new Zn based electrode materials have been fabricated with different

synthesis techniques and the results are reported and summarized in this thesis.

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Chapter No. 2

Chapter No. 2 Review of Literature

34

2 REVIEW OF LITERATURE

2.1 Introduction

This chapter contains a detailed literature survey that extends over the past

twenty years to understand the present status of fuel cell technology, particularly solid

oxide fuel cell. The main theme in this literature leads to reduce the manufacturing

cost and the working temperature to commercialize the fuel cell technology, which

could provide neat and clean, pollution free, stable and high performance fuel cell for

new generations.

2.2 Background of Solid Oxide Fuel Cell

Solid oxide fuel cells are widely the competent strategy which converts chemical

energy directly into electricity alongwith heat and power as a by-product without

combustion. At the end of nineteenth century, basically, Nernst and his colleagues [1-

3] proposed this idea in the University of Gottingen, Germany. Even 100 years after

the first discovery of fuel cell, considerable advances in theory and experiments are

still being made by scientists and researchers. However, two scientists Baur and

Preis[4] finally decided the composition for electrolytic material used in fuel cell.

This material was composed of lithium zirconate, clay and Nernst-Mass (30% lithium

zirconate, 10% clay and 60% Nernst-Mass (85% ZrO2 and 15% Y2O3). However, it

was observed that this material was too expensive to put fuel cell in any commercial

use. A fuel cell system consisted of 85% ZrO2 and 15% CaO electrolyte with porous

platinum electrodes was developed by Weissbart and Ruka in 1958 at Westinghouse

Electric Corporation [6]. The cell was tested in temperatures range of 800 to 1100oC

with three fuels; i) pure hydrogen, ii) methane iii) mixture of methane, water and

nitrogen (3.8% methane, 2.1% water and 94.1% nitrogen). Fuel was supplied at the

anode side and pure oxygen at cathode side. He joined Siemens in 1998 and


35

established a Siemens-Westinghouse Power Corporation. The newly established

company focused on tabular SOFC concept and the development of planer fuel cell

technology was stopped by Siemens’ in-house. However, a tube type system was

introduced to market and developed whilst Entwicklungsgesellschaft Brennstoffzelle

GmbH and Fraunhofer-Istitute for Ceramic Technologies and sintered Materials,

Germany, IKTS developed the Siemens planar SOFC [4].

2.3 Components of Solid Oxide Fuel Cell

Fuel cell consists of three components

1) Anode 2) Electrolyte 3) Cathode

2.3.1 Review of Anode Component of SOFC

Many Ni based electrodes have been used with YSZ because Ni-YSZ cermets

have numerous wanted assets for SOFC anode due to capability of both electronic and

ionic conduction way via Ni metal and YSZ respectively [6]. Although, Ni based

anode exhibits excellent catalytic properties for the oxidation of fuel and provides

good results in current collection [7] yet it shows some disadvantages such as

poisoning in the form of sulphur, carbon deposition and poor oxidation stability which

are major drawbacks for volume stability [8]. In order to overcome these problems,

there is a great need to find out alternate anode materials which may improve the

stability of the cell as well as to increase the electronic and ionic conductivity. It is

suspicious that the anode microstructure contributes to enhance power density of solid

oxide fuel cell [9]. Zhu et al. [10] investigated that the composite of YSZ with Ni-

cermet and Sr doped LaMnO3 as anode and cathode respectively are the best

electrodes for SOFC. The electrodes consisted of Ni and LSM can be easily fabricated

and they offer reasonably good performance. Fang et al. [11] used Ni(NO3)2,

Sm(NO3)3 and Ce(NO3)3to make Ni-SDC composition by co-precipitation technique.


36

Ni-SDC cermet has an ability of two phases structure, on is cubic NiO and other is

fluorite structure of SDC. The results of DC conductivity of Ni-SDC anode was

measured by DC four-probe technique at hydrogen atmosphere and found to be 573

and 183 S/cm at temperatures of 500 and 800oC, respectively. The decreasing

conductivity Ni-SDC cermet with increasing temperature indicates its metallic

behavior. The maximum power densities were found to be 209, 306 and 388mW/cm2

in a temperature range of 650 to 750oC, with an interval of 50 oC. The open circuit

voltage was also measured 0.81, 0.84 and 0.95 V over the same temperature. Glycine

nitrate process technique was employed to prepare four different types of anode

materials using NiO as a major compound with the contribution of Ce0.9Gd0.1O1.95

(GDC) by Liu et al. [12].Maximum OCVs were found to be 0.93, and 0.84 V, while

power density of 220 and 402mW/cm2 at temperatures of 600 and 700oC,

respectively. A cost effective processing method to fabricate Ni cermet of Ni-SDC as

anode for ITSOFC was introduced by Misono et al. [13]. At first time, the powders of

SDC precursor and NiO precursor were mechanically indulgence to form composite

material of SDC and NiO. A ceramic tape casting technique was applied on the

composite powder to make a substantial layer for anode sustaining. A single cell was

constructed having three consecutive layers of Ni-SDC/SDC/LSCF to complete the

fuel cell. The maximum power density of 910mW/cm2 was obtained at 650oC. Huang

et al. [14] modified Ni/Scandia-Stabilized Zirconia (Ni-ScSZ) cermet anode instead of

Ni-SDC cermet by coating 2.0 wt.% nano-sized gadolinium-doped ceria (GDC) for

SOFC using a simple combustion process. They found that open circuit voltage and

power density were 1.027V and 584mW/cm2 at temperature 700oC without coating

SDC layer. They also observed that the modified anode ScSZ coated with 2.0% GDC

enhances the open circuit voltages (OCVs) as well as power out put from 1.027V to


37

1.078V and 584mW/cm2 to 825mW/cm2, when the working temperature of an SOFC

was raised from 700 to 850oC in 3% H2O hydrogen. A wet coating and succeeding

technique was applied to obtain an intense electrolyte layer on micro-tabular electrode

by Yamaguchi et al. [15]. A dense electrolyte of GDC and a multi layered structure of

porous LSCF-GDC on a substrate of NiO-GDC were used to fabricate micro-tubular

cell. They found that maximum power density 400mW/cm2 at 550 oC in wet H2 fuel

flow. Cho and Choi [16] prepared porous Ni-supported solid oxide fuel cells of

approximately 150µm film by the style casting on Nickel powder by coating yttria

stabilized zirconia electrolyte and Ni-YSZ cermet anode followed by sintering at 1400

°C in a falling temperature atmosphere. The OCV and power density of the cell were

calculated at 800oC. He used a cathode material of a composition of

La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF) with above anode and electrolyte. The single cell

exhibited an appropriate performance at 800oC for open circuit voltage (OCV) and

power density. The values of measurements were found to be 0.96 V and

470mW/cm2for open circuit voltage and power density, respectively. Hui et al. [17]

constructed an SOFC on porous stainless steel substrate with porous NiO–SDC as

anode alongwith SDC (electrolyte) and SSC (cathode). Tavares et al. [18] replaced

Ni-YSZ conventional anode with Cu-SDC anode using Ni-YSZ conventional anode

preparation technique. The cell having Cu based anode was tested with humidified

hydrogen and humidified methane fuel in a temperature range of 500-700oC. The

OCV values were found to be 1.05 and 0.9 V with H2 and methane fuel, respectively.

It was noted that both the fuels exhibited the same power density of 250mW/cm2.Feng

et. al. [19] prepared a Ni-YSZ cermetas deposited a multi-layer of Cu-CeO2on Ni-

YSZ to get high temperature solid oxide fuel cells. The stability and performance

were tested for these anodes in H2-CO syngas at 750oC. It was found that high


38

concentration of CO causes carbon deposition in Ni/YSZ anode and it produces

cracks in Nickel-Yttria Stablized Zirconia anode after long-term function. However,

an enhancement of its stability has observed due to Cu-CeO2 catalyst layer placed on

Ni-YSZ anode superficial part. The stability of an optimized single cell was further

tested by running it for 460 hours using a fuel in composition of 48.5%H2-48.5%CO-

3%H2O. During this experiment, no degradation was observed in its performance.

However, increasing the time more than 460 hrs upto 630 hrs, a carbon deposition

was observed on its anode and it forms successive cracks on anode. By virtue of this

factor, its performance has shown to drop upto a certain level. Liu et al [20] prepared

a composite anode of Ni + BZCY (65wt% NiO and 35 wt %). He then used it to

construct fuel cell with BZCY electrolyte and SFM cathode. A suspension coating

method was used to deposit BZCY electrolyte films on the anode substrates.

Electrochemical characterizations and fuel cell performance were analyzed

implementing a model of 3-400 test system (Princeton Applied

Research)VERSASTAT. AC impedance was deliberated in the frequency range from

0.01Hz to 100 kHz from 750oC to 850oC at an interval of 50oC at hydrogen and air

atmosphere. Millerand Irvine[21]prepared a new series of compound as alternate

anodes for solid oxide fuel cell using LSTX material. The used compositions are as:

La0.33Sr0.67Ti0.92X0.08O3+δ, (where X = Al3+, Ga3+, Fen+, Mg2+, Mnn+ and Sc3+). He

concluded that the structure, redox properties, conductivity and electro-catalytic

behavior of the compound depend on the dopant rate. Sengodan et al. [22] used tape

casting technique and a composite material of La0.8Sr0.2ScxMn1−xO3−δoxides LSSM

(where x = 0.1–0.3) as anode was synthesized. They impregnated 65% porous YSZ

for comparative low temperature solid oxide fuel cells. It has been found that new

composite anode can work directly on hydrocarbon fuels with high efficiency. The


39

highest power density of 341mW/cm2 was achieved at 700oC. FexCo0.5−xNi0.5Tri-

metal alloys were suggested as anode material by Xie et al. [23]. They used ceria

based gadolinium doped ceria having compositions Ce0.9Gd0.1O1.95 electrolyte.The

try-metal alloys were synthesized with glycine-nitrate technique. Two different cells;

symmetrical and single cell with SSC-SDC cathode: (Sm0.5Sr0.5CoO3)–SDC and GDC

electrolyte were made by co-pressing and co-firing technique. Interfacial polarization

resistances and I–V curves of these both type cells were measured at initial

temperature 450oC, 500oC and 550oC and then 600oC. It has been found that the cell

with Fe0.25Co0.25NiO0.50–SDC as anode exhibited the minimum interfacial resistance

and maximum power density of 0.11Ωcm2 and 750mW/cm2 at 600oC, respectively

using humidified (3% watered hydrogen)H2as fuel and stationary air as oxidant as

compared to Ni-YSZ anode based fuel cell. Zhu et al. [24] prepared an anode matrix

by impregnating method using a porous yttria stabilized zirconia YSZ with a nitrate

aqua containing La3+, Sr2+, Cr3+, Fe3+, Ni2+ and urea for solid oxide fuel cell (SOFC).

The methane oxygen gas mixture was used to test the single chamber fuel cell with

YSZ membrane as the electrolyte and La0.8Sr0.2MnO3-δ (LSM) as the cathode. The

maximum power density of 214mW/cm2 was achieved at an operating temperature of

800oC, when the CH4 to O2 gas composition was 2:1. A new versatile technique of

combustion of nitrate-glycine gel to form NiO-YSZ powder was developed by

Kakade et al. [25].They found that the ability to be dense increases with adding thye

soaking time as they observed a reduction of porosity of the specimen.

The present work deals with solid oxide fuel cell (SOFC) having many new Zn

based nano-structured anodes. The nano-structured anodes based on Zn offer

reasonably good performance at comparatively low temperature (400-550oC) [26].

The optimized nanostructure electrode enhances the SOFC performance at low


40

temperature; also they can be fabricated easily by different techniques. The major

challenge for the SOFC community is to improve electronic conductivity in electrode

material and to reduce it in electrolyte material. For this purpose, new Zn based

anodes have been prepared at low manufacturing/sintering temperature. The doped

ceria produces oxygen vacancies which will enhance the oxygen conductivity at low

temperature in the range of 400-600oC [27]. Our focus is to develop compatible

composite anodes for low temperature solid oxide fuel cell (LTSOFC), which would

give high performance in the temperature range of 400-550oC. Mixed anodes capable

of yielding both electronic and ionic conductivities may be a possible solution. To

verify this assumption, mixed anodes consisting of Zn based anodes and ceria based

electrolyte material in appropriate weight ratio were prepared and their performance

was investigated.

2.3.2 Review of Electrolyte Component of SOFC

The electrolyte material is considered to be the heart of a solid oxide fuel cell [28].

The challenges, problems and difficulties over 100 years faced with respect to the

electrolyte could be solved by introducing new electrolyte materials showing oxygen

ion conduction. These new electrolytes must execute ionic conductivity of 0.1S/cm,

which is the basic requirement of SOFC. Conventional SOFC based on yttrium

stabilized zirconia (YSZ) electrolyte material, is carrying out at 1000oC but such a

high temperature is a main barrier in the commercialization of SOFC technology. It is

a big challenge to lower the operating temperature in order to commercialize the solid

oxide fuel cell. This can be achieved only through state of the art nanotechnology.

Sincesingle phase electrolyte can not provide a basic required ionic conductivity at

low temperature, hence two phase composite electrolyte could be a better approach to

achieve the goal using nanotechnology. For this purpose, Solid Carbonate Ceria


41

Composite (SCCC) electrolytes were prepared. It was discovered that theses materials

yield high ionic conductive 2 S/cm at a temperature 600oC. The result of conductivity

ensures that these materials could be utilized in low temperature solid oxide fuel cell

[29-30].

There are many electrolyte candidates such as yttria stabilized zirconia YSZ,

doped ceria oxide (DCO) and doped bismuth. Among these electrolytes, first two

electrolytes (YSZ and DCO) are mostly used for solid oxide fuel cells. The YSZ

electrolyte used in SOFC typically works in the temperature range 800-1000oC [31].

Many ceria based new electrolytes were developed which yielded 0.1S/cm ionic

conductivity in the temperature range of 400-600oC, which is comparatively low

temperature than that of the ionic conductivity of YSZ electrolyte. SDC, GDC and

CDC are the most popular electrolytes, which exhibit 0.1 S/cm ionic conductivity in

temperature range of 400-550oC [32-37]. Experimentally, the ionic conductivity of

pure ceria has been found very poor. However, its ionic conduction can be enhanced

by doping bivalent or trivalent oxides like Ca, Sm and Gd etc. [38-39]. The doped ion

ceria is a major candidate to minimize the operational temperature at a certain level

for solid oxide fuel cell [40]. The fuel cell composed with this electrolyte exhibits

power densities 200-600mW/cm2 and current densities 300-1200mA/cm2 in the same

temperature range i.e. (400-600oC). It has been noted that solid carbonate ceria

composite SCCC electrolyte shows two phase conduction (i) oxygen ions originating

from ceria phase (ii) proton from the carbonate phase. Enoki et al [41] investigated

LSGFM material as electrolyte for SOFC having composition in molar ration (as

La:Sr:Ga:Fe:Mg = 0.7:0.3:0.7:0.2.:0.1). The open circuit voltage OCV was found to

be 0.8 V which was low. He pointed out that the anode material affects the open

circuit voltage strongly and the highest OCV can be obtained by using Ni-Fe


42

bimetallic anode. The oxide ions films (YSZ, SDC and LSGM) were coated on anode

material to enhance the power density. The power densities of these coating films

were to be had following order: LSGM>SDC>YSZ. The LSDM film was growth by

PLD deposition technique on LSGFM plate. The highest power densities of 197 and

100mW/cm2 were achieved at 600oC and 500oC, respectively. Therefore, LSGFM

works as an electrolyte material for SOFC. BZCY7 electrolyte was prepared by Zuo

et al. [42] for solid oxide fuel cell. He measured the ionic conductivity of BZCY7

electrolyte at 550oC and found to be 9 x 10-3S/cm. They then compared it with that of

three conventional electrolytes; YSZ, LSGM and GDC and the ionic conductivity of

BZCY7 was to be found higher than that of YSZ from 300 to 700oC temperature. The

maximum power density was found to be 270mW/cm2 at 700oC.Ma et al [43]

developed novel core–shell nanocomposite electrolyte material of Ce0.8Sm0.2O1.9:

Na2CO3by co-precipitation method. Where Na2CO3 is an amorphous core on SDC

cubic fluorite.In this way, super ionic conductivity of electrolyte has been obtained at

300oC. Nanocomposite electrolytes having such a high ionic conductivity were

employed as electrolyte material in low temperature solid oxide fuel cells (LTSOFCs)

using NiO and lithiated NiO as anode and cathode, respectively. They recorded a

highest power density of 800mW/cm2 at 550oC. She suggested a promising electrolyte

material which can work at low temperature for solid oxide fuel cells. She named

SDC/Na2CO3 composite as core–shell nano-structure. It has been demonstrated that

nano-structured material has stability that might be double even at high temperature

due to their high surface energy. The peak power density was achieved 780mWcm/2

at 550oC and a continuous output of 620mW/cm2 was obtained during 12 hour

continuous operation. The ionic conduction of two phase ceria carbonate composite

was further studied experimentally byRaza et al [44] and concluded that ionic


43

conductivity can be enhanced especially adopting nano scale technique. Xia et al. [45]

examined the ternary eutectic carbonate phase way (10, 30 and 50 wt. %) affects on

the performance of a composite SDC electrolyte. The compositions having 30 and 50

wt. % carbonate showed an increase in conductivity with respect to the composition

which is that had 10 wt. % at 400oC close to the melting point of the eutectic

carbonate. This temperature is more than 100oC lower than binary carbonated

electrolyte. The fuel cell consisted on ternary carbonated SDC fuel cell exhibits a

power density of 720mWcm-2 and current density 1300mAcm-2 at 650oC, using

CO2/O2 as cathode gas. Water was observed at both anode and cathode outlet gas

terminals and CO2 was only detected in the anode outlet gas. This proposed ternary

scheme and CO2 in the cathode gas extensively enhances the power density and

stability of the single cell. The structure and A.C. impedance spectra of various ceria-

based composite systems were analyzed by Tang et al. [46]. They observed from

structural studies that the carbonated ceria composite has two phases; doped ceria is

the 1st phase and carbonates were the 2nd phase. The 2nd phase was often found to be

amorphous. In view of NANOCOFC (nano-composites for advanced fuel cell

technology) approach, ceria and carbonates are combined in two phases such as ceria

is 1st phase and carbonate is 2nd phase at various particle size levels.

2.3.3 Review of Cathode Component of SOFC

The lanthanum manganese oxide (LaMnO3) material is a most commonly

used cathode, which is often doped with rare earth material (Sr, Ce or Pe etc.) to

enhance its conductivity. Usually, it is doped with strontium (Sr) and is referred to as

LSM. The cathode has probably perovskite structure with pure electronic conductivity

and no ionic conductivity at all. There are many cathode materials such as BSCF,

LSCF, LSM, SSC and GBC, which are used for low temperature solid oxide fuel cells


44

(LTSOFC) [47-56]. LSCF cathode is one of the best promising cathode material used

for solid oxide fuel cell (SOFC) having intermediate temperature range from 600 to

800oC. Lanthanum (La) could be replaced by Barium (Ba) to develop a new BSCF

cathode for LTSOFC exhibiting a numerous advantages like high electronic

conductivity, outstanding oxygen transport phenomenon and catalytic activity [53, 57-

58]. Murray and Barnett [59] evaluated the smallest polarization resistance of a

composite of LSM-GDC cathode and YSZ electrolyte. The value of measurement was

observed to be 0.49 Ωcm2 at 750oC. Dusastre and Kilner [60] also reported that the

resistance between LSCF-SDC cathode and SDC electrolyte increases from about

0.2Ωcm2 to 10Ωcm2 during the fall in temperature from 600oC to 500oC. However,

the smallest value of 0.18Ωcm2 has been observed for interfacial resistance at SSC-

SDC cathode and SDC electrolyte at 600oC [52]. Three different cathode materials of

BSCF, SSC and LSCF were prepared by sol-gel technique having compositions

Ba0.5Sr0.5Co0.8Fe0.2O3-δ, Sm0.5Sr0.5CoO3-δ and La0.6Sr0.4Co0.2Fe0.8O3-δ byShao et al.

[52].Theperformance of the BSCF cathode was tested in a conventional, dual chamber

using SDC as the electrolyte. The maximum power densities of 1010mW/cm2 and

402mW/cm2 were achieved at 600oC and 500oC respectively. The area specific

resistance ASR was found to be 0.021Ω/cm2 at 600oC, and 0.135Ω/cm2 at 500oC. The

double perovskite cathode materials GdBaCo2O5+xwere developed by Chang et al.

[61] for intermediate temperature solid oxide fuel cells (ITSOFC). The performance

of its electrode materials were measured a temperatures T < 700°C using AC

impedance spectroscopy technique. It has been observed that GdBaCo2O5+x cathode

materials exhibits a small value of 530mΩcm2 of area specific resistance (ASR) at

918 K. Wei et al. [62] prepared BSCF-xSDC composite cathode material with

composition of Ba0.5Sr0.5Co0.8Fe0.2O3−δ – xSm0.2Ce0.8O1.9(where x=0–60 wt. %) using


45

soft chemical methods. The improvement in electrochemical properties has been

observed by adding different weight percentage of SDC electrolyte into BSCF

cathode. He used two different techniques one is DC polarization and second one is

AC impedance spectroscopy technique for electrochemical properties measurements.

However, it was observed that the addition of 30 wt. % of SDC into BSCF (70 wt. %

BSCF + 30 wt. % SDC) shows 5.5 times higher current density with respect to pure

phase of BSCF cathode (100wt% BSCF + 0wt%SDC) at 550 °C with additional

advantages of polarization resistance. A lot of efforts were made by Mat et al. [63] for

the development of such cathode materials which are compatible to ceria-carbonate

composite (CCC) electrolytes. For this purpose, a variety of cathode materials were

prepared, BSCF perovskite oxide, LFN (LaFeO-based oxides, e.g. LaFe0.8Ni0.2O3)

perovskite oxides, binary or ternary phase metal oxides were primarily cathode

materials which were investigated. He observed that the three phase metal oxide

cathode of CuNiOx–ZnO exhibited the highest power density of 500mW/cm2 at 850

K. The composite cathodes of BSCF-LSGM having compositions of

Ba0.5Sr0.5Co0.8Fe0.2O3−δ–La0.9Sr0.1Ga0.8Mg0.2O3−δwere synthesized by Liu et al. [64]

using combustion synthesis method. The chemical compatibility of the BSCF with

LSGM exhibited excellent results when 40 wt. % LSGM is mixed with BSCF. Wang

et al. [65] investigated the properties and measured the performance of composite

cathode with 70 wt. BSCF and 30 wt. % SDC for solid-oxide fuel cells in the

temperature range of 600-800oC. The area specific resistance of BSCF-SDC

composite cathode was found to be ∼0.064Ωcm2 at 600oC, which is slightly greater

than that for BSCF. The maximum power densities of ∼382mW/cm2and 1050 were

achieved at 500 and 600oC respectively, using thin-film electrolyte with the BSCF-

SDC composite cathode ablaze at 1000oC. The SrSc0.2Co0.8O3-δ (SSC) perovskite as


46

a cathode material was investigated byZhou et al. [66]for low temperature solid oxide

fuel cell. In SSC composition, the thermal expansion coefficient was trim down by

doping Sc. This SC doping also creates extremely high number of oxygen vacancies

in the lattice at low temperature. The area specific resistance ASR of SSC cathode

material was measured to be 0.206 Ωcm2 at 550oC, which is about 52% lower than

Ba0.5Sr0.5Co0.8Fe0.2O3-δ BSCF cathode. The maximum power density of 0.546W/cm2

was achieved at 500oC based on a 20µm thick SDC electrolyte. The novel cathodes of

BaCo0.7Fe0.3-yNbyO3-δ oxides (y = 0.00–0.12) were developed byZhu et al. [67]using

conventional solid state reaction process for intermediate temperature solid oxide fuel

cells (IT-SOFCs). The high stability of BCFNy was found in Nb concentration, higher

than y≥0.04. The unit cell volume increased at y = 0.10, and beyond this it decreased.

The electrochemical properties can be significantly enhanced by niobium doping in

BCFNy materials. The smallest interfacial resistance was calculated in BCFN0.10

composition among all the compositions. The maximum power densities were found

to be 202, 350, 569, 820, and 1006mW/cm2 at 600, 650, 700, 750, and 800oC,

respectively.

In order to minimize interfacial resistance, new composite cathode materials of

Ba0.4 Sr0.6Co0.3Mn0.7O3-δ- BSCM and La0.1Sr0.9Co0.2Zn0.8 LSCZ were developed in our

research work: Ferric Fe was replaced by Mn in BSCF cathode. The replacement of

Fe by BSCF can decrease the interfacial resistance by more than 50%. This reduction

in area specific resistance (ASR) can cause an enhancement of power density at

comparatively low temperature (400-550oC). This achievement of low interfacial

resistance between BSCM-NKCDC cathode and NK-CDC electrolyte could be

obtained by adopting nano-scale manufacturing technique for the preparation of

BSCM and LSCZ cathode materials. Nano-structured cathode provides the best high


47

way to transport the ions through the interface and helps the electrons to move

through the external circuit. This nano-structured skill is the most promising driving

force to boost the conductivity as well as performance of the cathode material at

comparatively lower temperature [68].

2.3.4 Review of Cost Comparison of Electrode Materials for SOFC

Rivera et al. [69] reported and presented the cost of solid oxide fuel cell and

combined heat and power CHP SOFC system with an electric capacity of 1 and 250

kW. Actually authors wanted to explore the cost breakdown of production cost so he

developed a model of manufacturing cost of the components (anode, electrolyte,

cathode and interconnectors) of SOFC. The raw material, energy, labor and capital

charges were included in this model to interpret the manufacturing cost for

production[69]. Through various literature surveys, it is outlined that the Hydrogen

Fuel Cell HFC is slowly making its importance into the transportation energy mix. It’s

benefits seem manifold: Hydrogen Fuel Cells release only water vapor, and once

generated. It also can be supplied very quickly to a vehicle, and provide more range

per “fill up” than most current battery technologies.

In view of carrying all the CHP benefits, a number of questions can be raised: for

example; Yet, why isnot there a fuel cell in every car by now? More to the point, if

Fuel Cells can be used to generate emissions free electric mobility, why aren’t we

using the technology to generate cleaner grid power?

If researchers think to answer the above quarries, the answer states that, the public’s

safety concerns about hydrogen as a power source is very important, the Fuel Cell’s

lack of technology maturity, and the cost of building out an enhanced fuel delivery

and storage infrastructure, each kept Fuel Cells from moving middle-of-the-road.


48

From the above discussed three barriers, one large barrier to entry for a Hydrogen

Fuel Cell is the catalyst. Presently, most catalysts are made from Platinum(Pt) or its

alloy which is quite infrequent and therefore costly ($50,000 per kilogram). Hydrogen

Fuel cells which require a platinum catalyst remain a very high cost solution.

Let the problem be solved for the moment about the expensive platinum catalyst,

there still remain the issues of cost and sustainability as well as the concomitant

hydrogen generation, transport and storage challenges [70].Berkeley Lab researchers

did a lot of work to reduce the present cost of solid oxide fuel cell. They succeeded to

replace ceramic electrodes into stainless steel electrodes that are stronger, easier to

manufacture, and most importantly, cheaper. The last benefit can be proving a fruitful

turning point in the push to develop commercially viable fuel cells [71]. The target is

to reduce the cost of fuel cell of $400/kW [72].

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Conference 2010 [70] http://theenergycollective.com/cm1701/85113/renewable-energy-fuel-cells-part-2-

solid-oxide-comes-age dated 28-02-2013 [71] Krotz, D., Barkeley Lab, Almost there: a commercially viable fuel cell, 2002 [72] Source: Energy Information Administration, Annual Energy Review, 2007

Chapter No. 3

Chapter No.3 Characterization Tools

52

3 CHARACTERIZATION TOOLS

In order to analyze and characterize the material used for solid oxide fuel cells

(SOFCs), the following tools/techniques have been used as per requirement;

X-Ray Diffraction (XRD)

High Performance Scanning Electron Microscopy (HP SEM)

High Resolution Transmission Electron Microscopy (HR TEM)

Differential Scanning Calorimetery (DSC)

AC Electrochemical Impedance Spectroscopy (AC EIS)

3.1 X-Ray Diffraction (XRD)

In order to analyze the structure of the material, XRD pattern of sintered powders of

all the samples were obtained by implementing the Philips X'Pert X-Ray

Diffractometer fitted with an X'Celerator detector. Ni filtered and Cu Kα radiation

(λ=1.54056 Å) were used in flat plate θ/θ geometry. The data of X-rays was recorded

between 5 < x < 80, where x is the measure of angle in degree. The scan rate of 100 s

per step was controlled in steps of 0.02° at room temperature. The crystallite sizes

(Dβ) of each material were calculated using the peaks of line-broadening

measurements and Scherer’s equation was implemented for calculation as;

0.9

Where λ is the wavelength and β is the full width and half maximum (FWHM).


53

Figure 3.1: Philips X'Pert X-Ray Diffractometer [2]

3.1.1 Determination of Crystal Structure

There are three most important ladders as given below, to determine the

structure of a material from an XRD pattern.

The nature and range of the unit cell are realized from the angular position of

the diffraction lines. It is assumed firstly, that where does the unknown

structure lie from basic seven crystal systems? The respected miller indices are

allotted on behalf of the assumption. This step is called indexing and is

possible only when the correct possible choice of crystal system has been

made. Once this is finished, the shape of the unit cell is confirmed

The number of atoms in a unit cell is then yielded results from the shape and

range of unit cell, the chemical composition of the specimen, and measured

density.

Finally, the arrangement of atoms inside the unit cell is presumed from the

relative intensities of diffraction lines.


54

The XRD analysis follows the Bragg’s Law

3.1.2 Bragg’s Law

Bragg's Law describes a simple equation:

2dsinθ = nλ (ii)

The above equation explains why X-Ray bean is reflected by the act of splitting from

the faces of crystalsat definite angles of incident (θ). The inter-atomic distance

between the layer in a crystal is denoted by ‘d’and lambda λ is known as wavelength

of the incident X-ray beam while n stands for an integer.

Figure 3.2: Bragg’s Law Patterns for XRD [3]

3.2 Scanning Electron Microscopy (SEM)

A highly energetic electron’s beam is used to analyze the item on extremely

scale upto nano scale in electron microscopes.It (SEM) analyzes topographies of

materials with a magnifying series that envelop optical microscopy.The sample’s

surface can be scanned by scanning electron microscope (SEM) and electron beam

produces an image from the beam-specimen interactions that is detected by an ample

array of detectors. A bunch of detectors is existingfrom the source of secondary


55

electron detectors and this phenomenon provides surface information. A backscattered

detector contains compositional information in both maximum and minimum vacuum

modes. Following information can be extracted from the images obtained with the

help of an SEM.

3.2.1 Topography

Topography means that the surface facial appearance of an entity or "how it

looks", its grain; direct relationship between these texture and materials characteristics

(stiffness, reflectivity...etc.).

3.2.2 Morphology

The shape and particle size can be found in this section of morphology that is

made by object. There is a direct relationship between these texture and materials

characteristics (ductility, stiffness, reactivity...etc.).

3.2.3 Composition

Each element presented in the sample as well as their relative quantity is

detected by scanning electron microscopy SEM.Some material properties like

stiffness, melting point, stimuli etc. be contingent on the compositions of the samples.

3.2.4 Crystallographic Information

SEM analyzes that how the atoms are ordered in a crystal. A direct

relationship between these and characteristics of the materials like ability to transform

electricity can be observed.


56

Figure 3.3: Scanning Electron Microscope

3.3 High Resolution Transmission Electron Microscopy (HR

TEM)

Transmission Electron Microscopy (TEM) and Scanning Transmission

Electron Microscopy (STEM) both have the equivalent systems. TEM and STEM

both use an electron beam for sample’s reflection.These excited electrons, strikes on

ultra-thin specimen and grant permission for capturing resolutions in the range of the

order of 1-2Å. HR TEM possesses excellent 3-dimensional resolution, and has a

capability of further analytical measurements [4]. The assets of information

sequentially available from these trialsare extraordinary. With this technique, we can

not only acquire excellent picture resolution, yet it has also a potential to illustrate

crystallographic phase and orientation, dictionary of elements through EDX and

emphasized constituent of elements contrast (dark field mode). The entirenano meter

(nm) sized areas can be precisely located.


57

This technique has following characteristics;

It identifies the size of imperfection in nano scale on integrated circuits,

together with rooted particles and scum at the floor of a vial.

Crystallographic phases can be determined from an interface with a function

of distance.

Nano-particle characterization: Core/shell investigations, agglomeration,

effects of annealing.

Catalyst support coverage and ultra small area of element roots.

Figure 3.4: Transmission Electron Microscope [5]

3.4 Differential Scanning Calorimetry (DSC)

Differential Scanning Calorimetry (DSC) is a unique tool that analyzes the

thermal characteristics of the material. DSC instruments are used to understand

the required amount of heat for the preparation of the sample. It characterizes the

materials by three dimensional symmetrical constructions with homogeneous

heating system. It gives experimental results in a curve of heat fluctuation against

temperature or time. Enthalpy of transition can also be calculated with the help of


58

this curve by using a formula; H = kA (iii)

In the above equation, H is change in enthalpy; k is known as calorimetric constant

and A exhibits the area within curve. The oxidation and other chemical reactions can

also be studied by using DSC technique.

Figure 3.5: Differential Scanning Calorimetric Analyzer (DSC 404 F3 Pegasus) [6]

3.5 AC Electrochemical Impedance Spectroscopy (EIS)

AC Electrochemical Impedance Spectroscopy (EIS) is a great pinpointing tool,

which is used to characterize the impedance of the material and provides us the

internal resistance, interfacial resistance of the material particular a solid oxide fuel

cell. AC conductivity can also be measured by using this technique with the variation

of temperature. Three loss sources are fundamental and vital sources; 1) loss of

voltage in fuel cells: 2) movement of charge or “kinetic” losses; 3) “ohmic” losses,


59

and deliberation or “mass transfer” losses. This modern techniqueis used to analyze

the limitations and performance of the fuel cells and can also be used to take apart and

compute the font of polarization. AC Impedance Spectroscope is the best tool which

is used for research and development (R & D) area, structure of electrode. This also

can be used for product verification and quality assurance in assembling and process.

3.5.1 Instrumentation for Basic Measurements

In order to measure of ionic or electronic AC conductivity of the material, an

AC impedance instrument of VERSASTAT2273 galvanostatewas used. The

frequency range is adjusted between 0.01 Hz to 1 MHz. This instrument can be also

used to analyze the impedance spectra of the different materials under various

temperatures. The inductive, resistive and capacitive behavior as well as impedance of

the cell can be determined by frequency response analyzer (FRA). The impedance

spectroscopy can be used to recognize and compute the impedance linked with

diverse processes in excess of broad range of frequencies [7].

With the help of this technique, almost a semi-circle curve was drawn during

the impedance spectra with frequency from 0.01Hz to 1MHz. This curve consists of

real part of Z Impedance (Zre) versus imaginary part of Z Impedance (Zim) data which

shows the impedance spectra with the variation of frequencies at different

temperatures. By implementing the simulated curve using ZSim-Demo 3.20 software

containing a series of equivalent circuits of different models represents a network of

resistors, capacitors and inductors.We can collect significant qualitative and

quantitative information with respect to sources of impedance of fuel cell.


60

Figure 3.6: VERASTAT2273 Potentiostat (Princeton Applied Research, USA) [8]

References

[1] Cullity, B. D. “Elements of X-Ray Diffraction” 2nd Edition, Addison-Wesley

Publishing Company, Inc. ISBN 0-201-01174-3.

[2] http://www.panalytical.com/index.cfm?pid=321 dated January 27, 2011.

[3] http://hyperphysics.phy-astr.gsu.edu/hbase/quantum/bragg.htm; dated January

27, 2011.

[4] http://www.eaglabs.com/techniques/analytical_techniques/tesssm_stem.php:

dated January 27, 2011

[5] htp://www.google.com.pk/#hl=en&rlz=IR2ADRA_enSE394&q=photographs+;

dated February 22, 2011.

[6] http://www.netzsch-thermal-analysis.com/en/products/detail/pid,45.html; dated

January 27, 2011.

[7] http:/www.scribner.com dated February 20, 2011.

[8] VERSASTAT2273 potentiostat (Princeton Applied Research, USA) Software

Manual.

Chapter No. 4

Chapter No.4 Experimental

62

4 EXPERIMENTAL

4.1 Introduction

It is known that a fuel cell consists of three components anode, electrolyte and

cathode. This chapter explains how these materials were prepared. Different

experimental approaches were utilized for preparing these components. The method

used for preparing a particular material was selected and finalized after study the

various parameters such as maximum voltage and power density. The materials

showing good results were further studied with respect to their structure, particle size,

and impedance spectra and electrical conductivity.

4.2 Materials and Equipments

4.2.1 Chemicals

The chemicals used to prepare anode, electrolyte and cathode materials are

listed in different Tables 4.1 to 4.13 and the samples were assigned names. All the

chemicals as listed below were purchased from Sigma Aldrich USA.

4.2.2 Price List of the used Chemicals

The chemicals used to prepare electrodes (anode & cathode) and electrolyte

were purchased from the International chemical supplier Sigma Aldrich USA and

their price list has been illustrated in Table 4.14 to evaluate the ground cost of

electrodes on behalf the prices of raw materials, power utilization, researcher salary

and lab engineering etc.


63

Table 4.1: Sample No. 1; Composition Detail of CNZGC (Anode Material)

Sr. No. Sample Category Wt. % age Compositions Molar Compositions 1 Dry-1 12.00% CuCO3Cu(OH)2

11.00% NiCO3 46.90% Zn(NO3)2.4H2O 06.20% Gd(NO3)3.6H2O 23.90% Ce(NO3)3.6H2O

Cu0.16Ni0.27Zn0.37 Gd0.04Ce0.16

2 Dry-3 09.95% CuCO3Cu(OH)2 10.80% NiCO3 42.35% Zn(NO3)2.4H2O 07.60% Gd(NO3)3.6H2O 29.30% Ce(NO3)3.6H2O

Cu0.14Ni0.27Zn0.34 Gd0.05Ce020


Cu0.12Ni0.22Zn0.29 Gd0.09Ce0.28

4 Dry-7 08.75% CuCO3Cu(OH)2

09.10% NiCO3 37.70% Zn(NO3)2.4H2O 17.30% Gd(NO3)3.6H2O 27.20% Ce(NO3)3.6H2O

Cu0.13Ni0.24Zn0.32 Gd0.12Ce0.19


Cu0.11Ni0.19Zn0.26 Gd0.10Ce0.34

Table 4.2: Sample No.2; Composition Detail of ANZ (Anode Material)

Sr. No. Sample Category Wt. % age Compositions Molar Compositions 1 44 (a) 13.05% Al(NO3)3.9H2O

04.15% NiCO3 82.80% Zn (NO3)2.6H2O

Al0.1Ni0.1Zn0.8

2 44 (b) 13.90% Al(NO3)3.9H2O 08.80% NiCO3 77.30 Zn (NO3)2.6H2O

Al0.1Ni0.2Zn0.7

3 44 (c) 14.90% Al(NO3)3.9H2O 14.10% NiCO3 71.00% Zn (NO3)2.6H2O

Al0.1Ni0.3Zn0.6

4 44 (d) 16.05% Al(NO3)3.9H2O 20.32% NiCO3 63.63% Zn (NO3)2.6H2O

Al0.1Ni0.4Zn0.5

5 44 (e) 17.38% Al(NO3)3.9H2O 27.52% NiCO3 55.10% Zn (NO3)2.6H2O

Al0.1Ni0.5Zn0.4

Table 4.3: Sample No. 3; Composition Detail of CMZ (Anode Material)

Sr. No. Sample Category Wt.%age Compositions Molar Compositions

1 CMZ 14.00% CuCO3.Cu(OH)2

16.00% Mn(NO3)2 70.00% Zn(NO3)2·4H2O

Cu0.2Mn0.2Zn0.6


64

Table 4.4: Sample No.4; Composition Detail of BCFZ (Anode Material)

Sr. No. Sample Category Wt. % age Compositions Molar Compositions 1 BCFZ-1 02.80% BaCO3

15.80% CuCO3.Cu(OH)2

02.50% Fe(NO3)3.9H2O 78.90% Zn(NO3)2.6H2O

Ba0.05Cu00.25Fe0.02Zn0.68

2 BCFZ-2 02.80% BaCO3


05.00% Fe(NO3)3.9H2O 76.40% Zn(NO3)2.6H2O

Ba0.05Cu00.25Fe0.04Zn0.66

3 BCFZ-3 02.80% BaCO3


07.50% Fe(NO3)3.9H2O 73.95% Zn(NO3)2.6H2O

Ba0.05Cu00.25Fe0.06Zn0.64

4 BCFZ-4 02.80% BaCO3


10.00% Fe(NO3)3.9H2O 71.50% Zn(NO3)2.6H2O

Ba0.05Cu00.25Fe0.08Zn0.62

5 BCFZ-5 02.80% BaCO3


12.50% Fe(NO3)3.9H2O 69.00% Zn(NO3)2.6H2O

Ba0.05Cu00.25Fe0.10Zn0.60

6 BCFZ-6 03.45% BaCO3


16.94% Fe(NO3)3.9H2O 60.29% Zn(NO3)2.6H2O

Ba0.05Cu00.25Fe0.12n0.58

Table 4.5: Sample No. 5; Composition Detail of BFTZ (Anode Material)

Sr. No.

Sample Category Wt. % age Compositions Molar Compositions

1 BFTZ 11.35% BaCO3 15.50% Fe(NO3)3.9H2O 04.60% TiO2

68.55% Zn(NO3)2.6H2O

Ba0.15Fe0.1Ti0.15Zn0.60

Table 4.6: Sample No. 6; Composition Detail of NK-CDC (Electrolyte Material)

Sr. No. Sample Category Wt. % age Compositions Molar Compositions 1 NK-CDC Ce(NO3)3.6H2O

Ca(NO3)2.4H2O Na2CO3& K2CO3

Ce0.8 Ca0.2 O1.9 and Na2CO3: K2CO3 (1:1)

Table 4.7: Sample No. 7; Composition Detail of GDC-Y2O3 (Electrolyte Material)

Sr. No. Sample Category Wt. % age Compositions Molar Compositions 1 Y-GDC Ce(NO3)3.6H2O

Ca(NO3)2.4H2O Na2CO3&Y2O3(20wt.%)

Ce0.8 Ca0.2 O1.9 and Y2O3


65

Table 4.8: Sample No. 8; Composition Detail of NKSDC (Electrolyte Material)

Sr. No. Sample Category Wt. % age Compositions Molar Compositions 1 NKSDC Ce(NO3)3.6H2O

Sm(NO3)3.6H2O Na2CO3&K2CO3

Ce0.8 Sm0.2 O1.9 and Na2CO3: K2CO3 (1:1)

Table 4.9: Sample No. 9; Composition Detail of NSDC (Electrolyte Material)

Sr. No. Sample Category Wt. % age Compositions Molar Compositions 1 NSDC Ce(NO3)3.6H2O

Sm(NO3)3.6H2O Na2CO3

Ce0.8 Sm0.2 O1.9 and Na2CO3)

Table 4.10: Sample No.10; Composition Detail of GDC (Electrolyte Material)

Sr. No. Sample Category Wt. % age Compositions Molar Compositions 1 GDC Ce(NO3)3.6H2O

Gd(NO3)3.6H2O Na2CO3 or K2CO3

Ce0.8 Gd0.2 O1.9

Table 4.11: Sample No. 11; Composition Detail of BSCM (Cathode Material)

Sr. No. Sample Category Wt. % age Compositions Molar Compositions 1 BSCM 21.20% BaCO3

34.00% Sr(NO3)2 23.35% Co(NO3)2.6H2O 21.45% MnCO3

Ba0.4 Sr0.6Co0.3Mn0.7

Table 4.12: Sample No. 12; Composition Detail of LSCZ (Cathode Material)

Sr. No. Sample Category Wt. % age Compositions Molar Compositions 1 LSCZ 07.00% La(NO3)3.6H2O

25.60% Sr(NO3)2

08.10% Co(NO3)2.6H2O 59.30% ZnCO3

La0.1Sr0.9Co0.2Zn0.8

Table 4.13: Sample No. 13; Composition Detail of BSCF (Cathode Material)

Sr. No. Sample Category Wt. % age Compositions Molar Compositions 1 BSCF 20.94% BaCO3

22.65% Sr(NO3)2 39.10% Co(NO3)2.6H2O 17.31% Fe(NO3)3.9H2O

Ba0.5 Sr0.5Co0.8Fe0.2


66

Table 4.14: Price List of Chemicals from Sigma Aldrich used in this Research Work

Sr. No.

Chemical Name Purity Case No. Weight (gram)

€ PKR

Chemicals for Anode Material

1 CuCO3Cu(OH)2 Regent grade 12830 500 88.50 11470.35

2 NiCO3 99.9% 544183 1000 130.00 16849.10

3 Zn (NO3)2.6H2O 98% Regent

grade 228737 500 43.90 5689.81

4 Ni(NO3)2.6H2O 99.999% 203874 100 269.00 34120.00

5 ZnCO3 ≥ 58% 96466 1000 75.00 9572.27

6 Al(NO3)3.9H2O 99.997% 229415 100 394.50 51130.55

7 Mn(NO3)2 99.99% 203742 100 394.50 51130.55

8 MnCO3 ≥ 99.9% 377449 1000 139.15 17743.85

9 BaCO3 99.98% 329436 100 246.10 31896.65

10 Fe(NO3)3.9H2O 99.99% 254223 250 668.00 86578.47

12 TiO2 ≥ 99% 14021 1000 56.00 7258.07

Chemicals for Cathode Materials

13 Sr(NO3)2 99.995% 204498 50 614.00 79579.62

14 Co(NO3)2.6H2O 98% 230375 500 856.00 110944.87

15 La(NO3)3.6H2O 99.99% 331937 500 527.00 68303.68

Chemicals for Electrolyte Materials

16 Ce(NO3)3.6H2O 99% 238538 500 159.28 20644.04

17 Ca(NO3)2.4H2O ≥ 99% C 1396 1000 101.00

13090.46

18 Na2CO3 ≥ 99% S 7795 1000 95.40 12312.86

19 K2CO3 ≥ 99% P 5833 1000 67.70 8774.50

20 Sm(NO3)3.6H2O 99.9% 298123 100 246.68 31971.82

21 Gd(NO3)3.6H2O 99.99% 451134 50 299.00 38752.94

22 Y2O3 99.99% 205168 250 379.00 48486.00


67

4.2.3 Experimental Accessories

Following accessories and materials were used during the research work;

Mortar

Pestle

Ceramic Crucibles and Spatulas

Graphite Carbon

De-Ionized Water

Filter Papers

pH Papers

Beakers

Water supply

Plastic Glass Bottles to store prepared powders

Power Supply

Digital Weighing Balance

Fluid Sucking Machine

Digital Furnace upto 1600oC

Rheostat

Magnetic Stirrer

Microwave Oven

Hydraulic Press

Stainless Steel Die having 13mm diameter

Stainless Steel Holder including Ag rings to test the cell

Fuel Cell Testing Unit (L-43 China)

Electronic Load (China)

Thermocouple

VERSASTAT 2273 Potentiostat (Princeton Applied Research, USA)

KD 2531 Digital Micro-Ohmmeter, China

Hydrogen Gas Cylinder with Regulator

Oxygen Gas Cylinder or High Pressure Air with Regulator


68

4.3 Identification of Raw Materials for Low cost Electrodes

Zinc nitrate is a colorless crystalline solid and soluble in water as well as alcohol.

The solubility of Zink Nitrate Hexahydrate Zn(NO3)2.6H2O in water is about 184.3

g/100ml at room temperature. Zink Nitrate is considered an oxidizing agent which can

be a fruitful candidate as anode materials for solid oxide fuel cell to oxidize the fuel

(hydrogen). Hydrogen (fuel) is provided at anode side of the solid oxide fuel cell

hydrogen atoms (fuel) dissolved into positive and negative ions. The fed fuel at anode

material losses electrons, and these electrons should be oxidized by anode material

(Zink is oxidizer). In order to perform this function, there must be an oxidizer. Zn is

also considered a transition metal and native doping of this semiconductor is n-type

and contains conductivity due to electrons. This conductivity is considered by virtue

of the stoichiometric excess of zinc ions that occupy interstitial locations in the crystal

lattice. However, its conductivity can be improved by doping other materials over a

very wide range. After heat treatment this Zn compound has been converted into ZnO

compound, which has numerous properties in material science. High electron mobility

is the unique property due to which Zn compound has been widely used as electrodes

application in the emerging field of solid oxide fuel cell. The fundamental principle of

the electrode (Zn based or Ni-YSZ cermet) is to carry on reaction between the

reactant (fuel or oxygen) and the electrolyte without itself being consumed or

corroded. It must also bring into contact the three phases i.e. the gaseous fuel, the

liquid or solid electrolyte and the electrode itself. The anode, used as the negative post

of the fuel cell, disperses the hydrogen gas equally over the whole surface of the

catalyst and conducts the electrons that are freed from hydrogen molecule, to be used

as a useful power in an external circuit. The cathode, the positive post of the fuel cell,

distributes the oxygen fed to it onto the surface of the catalyst and conducts the


69

electrons back from the external circuit where they can recombine with hydrogen

ions, passed across the electrolyte, and oxygen to form water. The catalyst is a special

material that is used in order to facilitate the reaction of oxygen and hydrogen.

Further, the present electrodes (Zn based electrodes) possess all those characteristics;

which are the fundamental requirements of solid oxide fuel cell.

4.4 Preparation Techniques

There are three components, which are used in solid oxide fuel cells. They are

named as anode, electrolyte and cathode materials. They were prepared by Solid State

Reaction (or Dry) Method, Co-precipitation Method and Wet Chemical Method

respectively.

These methods are explained below in detail.

4.4.1 Preparation of Anode Materials

4.4.1.1 Sample No. 1---------- Cu Ni Zn Gd Ce (CNZGC)

The CNZGC anode materials were prepared by solid state reaction method.

For this purpose, CuCO3.Cu(OH)2, NiCO3.2Ni(OH)2.4H2O, Zn(NO3)2.6H2O,

Gd(NO3)3.6H2O Ce(NO3)3.6H2O, (Aldrich Sigma USA) materials were employed

initially. These powders were mixed according to stiochometric ratio to obtain

different compositions as listed in Table 4.1. The mixture was then ground in a mortar

with pestle for one hour to make it homogenous. The homogenous precursors were

placed in a digital furnace and the temperature of furnace was allowed to raise

gradually upto 800oC. At this temperature, these powders were sintered for 4 hours.

The furnace was turned off and let it to be cool down to room temperature gradually.

A suitable amount of carbon (0.1wt. %) was then added to each sintered composition

to produce porosity. The mixtures were then ground for 10 minutes.


70

4.4.1.2 Sample No. 2 (a-e) ----------Al0.1 Nix Zn0.9-x (ANZ)

In order to prepare Al0.1NixZn0.9-x (ANZ) anode material for the fuel cell, solid

state reaction method was applied. Al2NO3, NiCO3 and Zn (NO3)3.6H2O (Aldrich,

USA) were manipulated as raw materials. The exact sample’s compositions of above

formula are illustrated in Table 4.2. These compositions can be described by a general

formula Al0.1NixZn0.9-x (ANZ) where x is varied from 0.1 to 0.5 with an interval of

0.1. The powders of the mentioned materials were combined in a ceramic bowl

(mortar) and ground with pestle for 1 hour to obtain homogeneity. Then these

homogenous powders of various compositions were put into furnace for sintering

process. They were sintered for 4 hours at 800oC. The furnace was then allowed to

cool to room temperature. A small amount of carbon (0.1wt. %) was mixed in sintered

powder to produce porosity. The mixture was then ground for 10 minutes to achieve

homogeneity.

4.4.1.3 Sample No.3 ---------- Cu0.20 Mn0.20 Zn0.60 (CMZ)

CuCO3.Cu (OH) 2, MnNO3 and ZnNO3·4H2O (Sigma Aldrich, USA) powders

were used to prepare the electrode. Solid state reaction method was applied to

synthesize the Cu0.2Mn0.2Zn0.6 O1.9 electrode. The appropriate molar ratio of Cu0.2

Mn0.2 Zn0.6 O1.9 was ground for one hour to produce homogeneity. The powder was

sintered at 800oC for four hours and then furnace was switched off to let it cool down

to room temperature. A small amount of carbon (0.1wt. %) was mixed in the sintered

powders and ground for 10 minutes to obtain better homogeneity. The detail of

composition is listed in Table 4.3.


71

4.4.1.4 Sample No.4 (a-f) ---------- Ba0.05 Cu0.25 Fex Zn0.7-x (BCFZ)

Ba0.05Cu0.25FexZn0.7-x where x = 0.02, 0.04, 0.06, 0.08, 0.10 and 0.12 (BCFZ)

anodes were successfully synthesized by dry method using different compositions.

The following materials of BaCO3, CuCO3.Cu (OH)2, Fe(NO3)2.9H2O,

Zn(NO3)2.6H2O purchased by Sigma Aldrich, USA were taken under experiments in

order to make anode materials. The stoichometric ratios of these precursors were

ground in a mortar with pestle to make the precursor homogeneous. These precursors

were placed in a furnace to sinter. The temperature of the furnace was raised

gradually upto 800oC and was kept constant at this temperature for four hours and

then allowed to cool the furnace to room temperature. The sintered powders were

again ground for 10 minutes by adding a small amount of carbon in order to provide

porosity. A detailed list of composition of each sample is listed in Table 4.4.

4.4.1.5 Sample No.5 ---------- Ba0.15 Fe0.10 Ti0.15 Zn0.60 (BFTZ)

The stoichometric ratio of BaCO3,Fe(NO3)2.9H2O, TiO2 and Zn(NO3)2.6H2O

(Sigma Aldrich, USA) were ground in a mortar with pestle to make the precursor

homogeneous. After grinding, this precursor was sintered at 800oC for 4 hour in a

digital furnace. The sintered powder was again ground for 10 minutes by adding a

small amount of carbon, which was used to produce porosity in the material. The

detail of composition has been shown in Table 4.5.

4.4.2 Preparation of Electrolyte Materials

4.4.2.1 Sample No. 6 - Sodium-Potassium Carbonated Calcium

Doped Ceria (NK-CDC)

Ce0.8 Ca0.2 O1.9 and Na2CO3: K2CO3 (NK-CDC) powder was prepared by co-

precipitation method. In order to prepare calcium doped ceria (CDC) powder,


72

Calcium Nitrate tetrahydrate Ca(NO3)2.4H2O (Sigma Aldrich, USA) and Cerium

Nitrate hexahydrate Ce(NO3)3.6H2O (Sigma Aldrich, USA) were dissolved into

1000ml of deionized water in 1:4 molar ratios under a vigorous stirring process

(800rpm) at 80oC. In order to coat a second phase on the CDC composite, Sodium

Carbonate Na2CO3 (Sigma Aldrich, USA) and Potassium Carbonate K2CO3 (Sigma

Aldrich, USA) powders were mixed as 1:1 (molar ratio) and dissolved into 500ml

deionized water under 1000rpm at 100oC for 30 minutes. The solution of both

carbonates was poured drop by drop into CDC solution keeping CDC: NK molar ratio

as 1: 2.5 and the stirring was continued for further two hours with 1200rpm at 150oC.

The pH value was noted to be 9. The precipitate was washed thrice with de-ionized

water and vacuum filtration machine of glass was used to obtain NK-CDC

agglomerate. This agglomerate was dried in an oven at 100oC over night and sintered

in a digital furnace at 700oC for 4 hours. This sintered powder was again ground for

homogeneity in a mortar with a pestle [1]. The detail of composition has been shown

in Table 4.6.

4.4.2.2 Sample No. 7- Gadolinium Doped Ceria Coated with

Yttrium Oxide (GDC-Y2O3)

Y-GDC electrolyte material was prepared by co-precipitation method.

Ce(NO3)3·6H2O and Gd(NO3)3·6H2O were used as starting materials. The

stoichiometric amounts of these powders were dissolved in de-ionized water. The

solution was mixedwith stirrer for approximately 30 minutes. Sodium carbonate

Na2CO3 solution was used as precipitation mediator under vital stirring, with molar

ratio (Ce3+Gd3+):CO3-2 = 1: 0.5. The precipitate was washed thrice with de-ionized

water to remove the carbonates and mud was obtained by vacuum filtration method.

The obtained mud was then dried at 80°C on hot plate over the night. Yttrium oxide


73

was dissolved in 100 ml of 0.05 mol /liter solution of the acetic acid CH3COOH. The

GDC powder was then mixed in yttrium oxide Y2O3 solution with a molar ratio of

80:20. The solution was again stirred mechanically and heated on a hot plate at 150°C

for 15 min to form the precipitation of white crystallites. The dried powder was

sintered for 4 h in a furnace at 750°C and ground for 1 h with mortar and pestle [2].

The detail of composition has been shown in Table 4.7.

4.4.2.3 Sample No.8- Sodium-Potassium Carbonated Samarium

Doped Ceria (NK-SDC)

Sodium-Potassium Carbonated Samarium doped Ceria NK-SDC electrolyte

powder was prepared by co-precipitation method. Appropriate composition of

Ce0.8Sm0.2O1.9 was used. The cerium nitrate hexahyderate Ce(NO3)3.6H2O (Aldrich

Sigma USA) and samarium nitrate hexahyderate Sm(NO3)6H2O (Aldrich Sigma

USA) were used as initial materials. The 20% Sodium:Potassium (1:1 molar ratio)

carbonates were used as second phase as reported in section 4.3.2.1. This electrolyte

has already been used for preparing fuel cell in our lab[3].The detail of composition

has been shown in Table 4.8.

4.4.2.4 Sample No. 9 - Sodium Carbonated Samarium Doped Ceria

(NSDC)

The NSDC composite powder was prepared by co-precipitation method with

appropriate composition of Ce0.8Sm0.2O1.9. The Ce(NO3)3·6H2O and Sm(NO3)·6H2O

were used as starting materials for electrolyte and 20 wt% Na2CO3 was coated on the

SDC composite. The detail of method of preparation has been elucidated in section

4.3.2.1 and the composition has been shown in Table 4.9.


74

4.4.2.5 Sample No. 10 - Gadolinium Doped Ceria (GDC)

The dry technique (solid state reaction method) was employed to prepare

Ce0.8Gd0.2O1.9 (GDC) powder. The Ce(NO3)3.6H2O and Gd(NO3)3.6H2O as the

starting materials with an appropriate molar ratio. The GDC ground powder was

sintered at 800oC for four hours. For details see Table 4.10.

4.4.3 Preparation of Cathode Materials

4.4.3.1 Sample No. 11 ---------- Ba0.4 Sr0.6Co0.3 Mn0.7 (BSCM)

The Ba0.4 Sr0.6Co0.3Mn0.7 composition was successfully synthesized by wet

chemical method. The following chemicals BaCO3,Sr(NO3)3, Co(NO3).6H2O and

MnCO3 were used at initiative step. About 10 wt % Oxalic Acid was employed as

precipitate agent. The appropriate materials were shacked by stirring at 100 rpm on

hot plate. After getting an agglomerate of BSCM, the powder was dried in open air

and placed into a digital furnace. The temperature was controlled at 800oC for four

hours. Then this sintered powder was ground in a mortar and pestle for 10 minutes

adding 0.1 wt. % carbons for porosity. A flow chart showing synthesizing process by

wet chemical method is depicted in Figure 4.1 and the detail of composition is given

in Table 4.11.

4.4.3.2 Sample No. 12 ----------- La0.1 Sr0.9 Co0.2 Zn0.8 (LSCZ)

The La(NO3)3.6H2O Sr(NO3)2, Co(NO3)3.6H2O and ZnCO3 were used as the

starting materials. The La0.1Sr0.9Co0.2Zn0.8 composition was synthesized by wet

chemical method and agglomerate of LSCZ powder was obtained followed by stirring

with 100rpm on hot plate. The mud of LSCZ was dried in open air followed by

sintering into digital furnace at 800oC for four hours. The sintered powder was again

ground in a mortar with pestle for 10 minutes adding 0.1 wt% of carbon to make it


75

porous. The flow chart of synthesizing process by wet chemical method is publicized

in figure 4.2 and the detail of composition is provided in Table 4.12.

4.4.3.3 Sample No. 13 ---------- Ba0.5Sr0.5C0.2Fe0.8 (BSCF)

The cathode material of Ba0.5Sr0.5Co0.2Fe0.8 was synthesized by wet chemical

method in which various amount of metal nitrates were dissolved in de-ionized water.

The oxalic acid was used as precipitant agent. The agglomerate of BSCF material was

obtained followed by stirring at 100rpm on hot plate. The agglomerate was dried in

open air. The material was sintered at 800oC for 4 hour [4-5]. The steps used for

synthesizing of BSCF cathode are shown in flow diagram (Figure 4.3) and the detail

of composition is listed in Table 4.13.


76

Figure 4.1: A Flow Chart for Synthesizing BSCM Cathode

3 layers Fuel Cell Performance

BaCO3 De-ionized water MnCO3

Sr(NO3)2 100ml/10g Co(NO3)2.6H2O

Addition of 10 wt.%

Oxalic Acid

Dry over the night at

open atmosphere

Sintering at 800oC

for 4 hrs

Grinding and obtained

BSCM Powder

Conductivity XRD/SEM

Grinding with the addition

of 20wt.% electrolyte and

0.1wt.% carbon

After 30 minutes

BSCM Powder

Multiple Steps

Sintering

Temp. 800oC Time 1 hr


77

Figure 4.2: A Flow Chart for Synthesizing LSCZ Cathode


La(NO3)3.6H2O

De-ionized water ZnCO3

Sr(NO3)2 100ml/10g

Co(NO3)2.6H2O

Addition of 10 wt.%

Oxalic Acid


open atmosphere

Sintering at 800oC

for 4 hrs


LSCZPowder




0.1wt.% carbon

After 30 minutes

LSCZ Powder

Multiple Steps

Sintering



78

Figure 4.3: A Flow Chart for Synthesizing BSCF Cathode


BaCO3 De-ionized water

Fe(NO3)3.9H2O

Sr(NO3)2

100ml/10g Co(NO3)2.6H2O

Addition of 10 wt.%

Oxalic Acid


open atmosphere

Sintering at 800oC

for 4 hrs


BSCFPowder




0.1wt.% carbon

After 30 minutes

BSCF Powder

Multiple Steps

Sintering



79

4.5 Preparation of Composite Anode and Cathode Materials

Composite anodes and cathodes were prepared by mixing in appropriate

proportion, electrode and electrolyte materials, whose preparation has already been

discussed in section 3.4.1 to 3.6.2. The scheme for each composite anode and cathode

is given in Table 4.15. These composite anodes and cathodes were used in

construction of fuel cell to test their performance.

Table 4.15: Scheme to Prepare Composite Anode and Composite Cathode Materials

Sr. No. Sample Category Electrode Electrolyte

01 Dry-1 80 wt. % Cu0.16Ni0.27Zn0.37 Gd0.04Ce0.16 20 wt. % NKSDC

02 Dry-3 80 wt. % Cu0.14Ni0.27Zn0.34 Gd0.05Ce020 20 wt. % NKSDC




06 44 (a) 80 wt. % Al0.1Ni0.1Zn0.8 20 wt. % GDC 07 44 (b) 80 wt. % Al0.1Ni0.2Zn0.7 20 wt. % GDC

08 44 (c) 80 wt. % Al0.1Ni0.3Zn0.6 20 wt. % GDC

09 44 (d) 80 wt. % Al0.1Ni0.4Zn0.5 20 wt. % GDC

10 44 (e) 80 wt. % Al0.1Ni0.5Zn0.4 20 wt. % GDC

11 44(f) 80 wt. % Al0.1Ni0.6Zn0.3 20 wt. % GDC

12 CMZ 80 wt. % Cu0.2 Mn0.2 Zn0.6 20 wt. % NSDC

13 BCFZ-1 80 wt. % Ba0.05Cu0.25Fe0.02Zn0.68 20 wt. % NK-CDC






19 BCFZ-5 80 wt. % Ba0.05Cu0.25Fe0.10Zn0.60 20 wt. % NSDC

20 BFTZ-NKCDC 80 wt. % Ba0.15Fe0.1Ti0.15Zn0.60 20 wt. % NKCDC

21 BFTZ-NSDC 80 wt. % Ba0.15Fe0.1Ti0.15Zn0.60 20 wt. % NSDC

22 NK-CDC 80 wt % Ni-cermet (Conventional) 20 wt. % NK-CDC

23 Y-GDC 80 wt % Ni-cermet (Conventional) 20 wt. % Y-GDC 24 Y-GDC 80 wt % Li-NiO 20 wt. % Y-GDC

25 BSCM 80 wt. % Ba0.4 Sr0.6Co0.3Mn0.7 20 wt. % NK-CDC

26 BSCM 80 wt. % Ba0.4 Sr0.6Co0.3Mn0.7 20 wt. % NSDC

27 LSCZ 80 wt. % La0.1Sr0.9Co0.2Zn0.8 20 wt. % NK-CDC

28 LSCZ 80 wt. % La0.1Sr0.9Co0.2Zn0.8 20 wt. % NSDC


80

4.6 Characterization of Samples

4.6.1 X-Ray Diffraction

In order to analyze the structure of the material, XRD pattern of sintered

powders of all the samples were obtained by implementing the Philips X'Pert X-Ray

Diffractometer fitted with an X'Celerator detector. Ni filtered and Cu Kα radiation

(λ=1.54056 Å) were used in flat plate θ/θ geometry. The data of X-rays was recorded

between 5 < x < 80, where x is the measure of angle in degree. The scan rate of 100 s

per step was controlled in steps of 0.02° at room temperature. The crystallite sizes

(Dβ) of each material were calculated using the peaks of line-broadening

measurements and Scherer’s equation was implemented for calculation as;

0.9

Where λ is the wavelength and β is the full width and half maximum (FWHM).

4.6.2 Microscopic Analysis

4.6.2.1 Scanning Electron Microscopy (SEM)

Philips XL-30 SEM was used for microscopic analysis of all the samples in terms

of size and shape of particles. It also gives information about the homogeneity of

particles.

4.6.2.2 Transmission Electron Microscopy (TEM)

The High Resolution Transmission Electron Microscope of model JEOL JEM-

2100F was used to analyze the microstructure and morphology of the material in

detail. This also analyses dimension, figure and arrangement of the particles. These

parameters develop a relationship to each other on the scale of atomic diameters.

However, TEM analysis was employed only for sample no. 6 named NK-CDC.


81

4.6.3 Differential Scanning Calorimetery (DSC)

The effect regarding heat was looked by DSC analysis (TA DSCQ2000) at the

temperature range 100–600°C with heating 20°C per minute of heating rate. This

thermal effect was studied in air atmosphere.

4.6.4 AC Electrochemical Impedance Spectroscopy (EIS)

Electrochemical impedance spectroscopy was employed at both hydrogen and air

atmosphere by using Auto VERSASATAT 2273 (Princeton Applied Research, Oak,

ridge, TN, USA). The frequency is changed from 0.01Hz to 1 MHz under 10mV bias.

Experimental and simulated curves were drawn in the light of EChem ZSimp Demo

version 3.20 Software by the adjustment of equivalent circuit LRQ(CR), where L, R,

Q and C represent the Inductance, Resistance, Charge and Capacitance of the

materials and used devices respectively.

4.7 Construction of Pellets for Conductivity Measurements

In order to measure the electrical conductivities of the electrode and electrolyte

materials, single layer pellets (13mm diameter and 3mm thickness) were prepared by

dry press technique using hydraulic press with a pressure of 280Kg/cm2. The prepared

pellets were then sintered for 1 hour controlling temperature at 700oC. In order to

establish electrical contact, both surfaces of pellets were painted by silver paste. The

pellet’s active area was fixed to be 0.64 cm2. The electrical conductivities were

measured in temperature range of 300-600oC. The Electrochemical Impedance

Spectroscopy (EIS) technique was implemented to measure AC conductivities of the

materials in both hydrogen and air atmosphere employing Auto Versa STAT 2273

(Princeton Applied Research). DC conductivities were also measured employing KD


82

2531 Digital Micro-ohmmeter, China. The following formula was used to calculate

the both type of conductivities;

Where σ is measured electrical conductivity, L indicates the thickness of the cell,

R exhibits internal resistance of the material while A is the proposed active area of the

cell.

4.7.1 Calculation of Activation Energy (Ea)

Activation Energy is defined as “the energy required for starting the chemical

reaction after employing the fuel (hydrogen) to the fuel cell. Activation energy for

each cell was calculated from conductivity measurements using Arrhenius plot. The

following formula has been used to derive its numerical value in electron volt.

exp

Where σ is conductivity, A is pre-exponential factor, k is Boltzmann’s constant,

T is absolute temperature in kelvin and Ea is the Activation Energy in eV. The value

of Boltzman’s Constant is 8.617x10-5 eVK-1.

4.8 Construction of Solid Oxide Fuel Cell

In order to understand the contribution of anode, cathode and electrolyte

materials, these materials were used in construction of solid oxide fuel cell.

Electrolyte material was sandwiched between two layers of anode and cathode. This

assembly (anode/electrolyte/cathode) was then pressed using a hydraulic press. The

pressure of the hydraulic press was maintained in the range 200-300Kg/cm2. For a

single cell test, a small pellet of size 13 mm diameters was made having an active area

of 0.64cm2. The thickness of the cell was controlled to be 0.8-1.0mm. The pressed


83

pellet was sintered at 650oC for 40 minutes. The silver paste was coated with brush on

both surfaces (anode and cathode) of the cell before going to performance test. In

order to make solid oxide fuel cell, a complete scheme for testing the performance of

the cell is shown in Table 4.16. A number of cells were constructed in this way and

tested to optimize their performance.

Table 4.16: Scheme to Prepare Complete Cell for Performance Measurements

Sample No. 1 CNZGC Composite Anode)

Cell No. Cell Category

Composite Anode

Electrolyte Composite Cathode

Thickness l (mm)

Pressure Kg/cm2

1 Dry-1 CNZGC NKSDC BSCF 1 270





Sample No. 2 (ANZ Anode)


Composite Anode


Thickness (mm)

Pressure Kg/cm2

6 44 (a) ANZ+GDC GDC BSCF 1 270

7 44(b) ANZ+GDC GDC BSCF 1 270

8 44(c) ANZ+GDC GDC BSCF 1 270

9 44(d) ANZ+GDC GDC BSCF 1 270

10 44(e) ANZ+GDC GDC BSCF 1 270

Sample No. 3 (CMZ Anode)


Composite Anode


Thickness mm)

Pressure Kg/cm2

11 CMZ CMZ+NSDC NSDC CMZ+NSDC 0.8 270

Sample No. 4 (BCFZ Anode)

Cell No. Cell Composite Electrolyte Composite Thickness Pressure


84

Category Anode Cathode (mm) Kg/cm2

12 BCFZ-1 BCFZ -1 +NKCDC

NKCDC BCFZ-1+NKCDC

0.9 220

13 BCFZ-2 BCFZ-2 +NKCDC

NKCDC BCFZ-2+NKCDC

0.9 220


NKCDC BCFZ-3+NKCDC

0.9 220

15 BCFZ-4 BCFZ-4+NKCDC

NKCDC BCFZ-4+NKCDC

0.9 220


NKCDC BCFZ-5+NKCDC

0.9 220


NKCDC BCFZ-6+NKCDC

0.9 220


NKCDC BSCF+NK-CDC

0.9 220

Sample No. 5 (BFTZ Anode)


Composite Anode


Thickness (mm)

Pressure Kg/cm2

19 BFTZ BFTZ+NKCDC NKCDC BFTZ+NKCDC

1 280

Sample No. 6 (NK-CDC Electrolyte)


Composite Anode


Thickness (mm)

Pressure Kg/cm2

20 NK-CDC Ni-NKCDC NKCDC Ni-NKCDC 0.8 200

Sample No. 7 (Y-GDC Electrolyte)


Composite Anode


Thickness (mm)

Pressure Kg/cm2

21 Y-GDC NiO-YGDC YGDC Li-NiO-YGDC

1 300

Sample No. 8 (NKSDC Electrolyte)


Composite Anode


Thickness (mm)

Pressure Kg/cm2

22 NKSDC Dry 1-9 NKSDC BSCF 1 270

Sample No. 9 (NSDC Electrolyte)


Composite Anode


Thickness (mm)

Pressure Kg/cm2

23 NSDC CMZ + NSDC NSDC CMZ+NSDC 0.8 270


85

Sample No. 10 (GDC Electrolyte) Cell No. Cell

Category Composite

Anode Electrolyte Composite

Cathode Thickness

(mm) Pressure Kg/cm2

24 GDC ANZ+GDC GDC BSCF 1 270

Sample No. 11 (BSCM Cathode)


Composite Anode


Thickness (mm)

Pressure Kg/cm2

25

SBCM

BCFZ-5 +NKCDC

NKCDC

BSCM+NK-CDC

0.9

280

Sample No. 12 (LSCZ Cathode)


Composite Anode


Thickness (mm)

Pressure Kg/cm2

26

LSCZ

BCFZ-5 +NKCDC

NKCDC

LSCZ+NK-CDC

1

280

Sample No. 13 (BSCF Cathode)


Composite Anode


Thickness (mm)

Pressure Kg/cm2

27 BSCF

CNZGC (1-9) NKSDC BSCF 1 270

28 BSCF

ANZ+GDC (a-e)

GDC BSCF 1 270

4.9 Fuel Cell Performance

Hydrogen gas was fed as a fuel and air is used as oxidant at the anode and

cathode side, respectively. The performance of the cell was measured under

unpredictable resistance load implementing testing unit of L-43, China. All the

measurements, data collection and result handling processes were completed under

the mechanism of computerized instruments. The H2 gas was allowed to flow in the

range of 100 to 110ml/min at 1 atmospheric pressure. The open circuit voltage (OCV)

and current was recorded for each resistance load in the temperature range of 400oC to

550oC. The values of recorded current were converted into current density having an

active are of 0.64cm2. The graphs were plotted current density versus OCV. From


86

these results, power density was also calculated and graphs were plotted current

density versus power density. Fuel cell testing holder is shown in Figure 4.4.

Figure 4.4: A Sample Holder for Fuel Cell Measurements

References

[1] Abbas, G., Raza, R., Chaudhary, M. A. and Zhu, B., Journal of Fuel Cell

Science and Technology, Vol. 8, Issue 5, (2011); Reference 041013.

[2] Raza, R., Abbas, G., Imran, S. K., Patel, I. and Zhu, B., Journal of Fuel Cell

Science and Technology, Vol. 8, Issue 5, (2011); Reference 041012.

[3] Raza, R., Wang, X., Ma, Y., Lia, X. and Zhu, B., International Journal of


[4] Bo, Y., Wenqiang, Z., Jingming, X. and Jing, C., International Journal of


[5] Baumann, F. S., Fleig, J., Habermeier, H-U. and Maier, J., Solid State Ionics,

Vol. 177, Issue 35-36, (2006); Pages: 3187-3197.

Chapter No. 5

Chapter No.5 Results and Discussion Sample No. 1

88

5 RESULTS AND DISCUSSION

5.1 Sample No. 1----------CuNiZnGdCe (CNZGC)

5.1.1 Introduction

In order to reduce the Ni element in the anode material, five different

compositions of this material were synthesized by solid state reaction method. These

compositions were named as Dry-1, Dry-3, Dry-5, Dry-7 and Dry-9. The purpose of

this study was to optimize the best composition in terms of performance as well as

conductivity. Among all the studied compositions, only one composition, Dry-7

exhibited high performance. The results of measurements as related to their structure,

particle size, electrical conductivity and performance are present and discussed below.

The whole work which is prescribed in this section (5.1) has been published in

Nanoscience and Nanotechnology Letter, Vol. 4 (2012), Pages: 389-393. This work

is related to study and optimization of different techniques and approaches to fabricate

electrode materials for solid oxide fuel cells and has been enclosed as an

ANNEXURE-1 on page XXIII.

5.1.2 Structural Studies

Figure 5.1 shows the X-Ray diffractometery of the various compositions of

CNZGC sintered at 800oC for 4 hours. The structure reveals that all the compositions

are crystalline and provides information that the composition consists of three phases

of NiO, NiZnO and gadolinium doped ceria (GDC) having rhombohedral,

orthorhombic and cubic fluorite system, respectively. A detailed chart of XRD

analysis has been shown in Annexure-4. In order to calculate the particle size of the

material, Scherer’s formula was applied. The particle size of NiO, NiZn and GDC

phases of each samples were calculated and listed in Table 5.1.


89

0 10 20 30 40 50 60 70 80 90

0

1000

2000

3000

4000

5000

6000

7000

Inte

nsi

ty

2θ2θ2θ2θ

Dry 1 Dry 3 Dry 5 Dry 7 Dry 9

♠

♠ ♥♥

♣GDC

♥NiO

♠NiZn

♣

♥

♠

Figure 5.1: XRD Patterns of CNZGCAnode Material (Sample Dry-1 to 9 Odd

Compositions)

Table 5.1: Crystallite Size Data of each composition of CNZGC

Sample Category

Sintering Temp. (oC)

Particle size of NiO (nm)

Particle size of NiZn

(nm)

Particle size of GDC

(nm)

Average ParticleSize (nm)

Dry-1 800 46.25 43.36 34.69 41.43

Dry-3 800 86.72 69.38 70.08 75.39

Dry-5 800 86.72 57.82 66.08 70.21

Dry-7 800 57.82 81.62 69.38 69.61

Dry-9 800 53.37 75.82 42.05 57.08


90

5.1.3 Experimental Set up

Figure 5.2 shows the experimental set up for conductivity and performance

measurements. The cell holder consists of two hollow chambers A and B. two

stainless steel pipes are connected to each chamber separately. One pair of pipes (one

from chamber A and other from chamber B) is used for supplying air or hydrogen and

the second one pair ofpipes is used for electrical leads. One silver ring is attached to

the lower surface of chamber A and other to the upper surface of chamber B for

providing good electrical contact.

Figure 5.2: Experimental Setup for Conductivity and Performance Measurements

5.1.4 Conductivity Measurements

The DC conductivity measurements were carried out of Dry 1-9 (odd

compositions) at both hydrogen and air atmosphere in the temperature range of 300-

600oC. The calculated values are listed in Table 5.2 and shown in Figure 5.3 and 5.4.

It has been observed that the DC conductivities of all compositions except Dry-7

composition is less than 0.3 S/cm, whereas, Dry-7 shows a conductivity value greater

than 4.5 S/cm. It has been suggested by Zhu [1] that the electrode conductivity should


91

be 10 times greater than the electrolyte conductivity used in a fuel cell.

Nanocomposite electrolyte NKSDC has conductivity 0.1 S/cm [2-7]. However, Dry-

7,CNZGC anode which contains 31 % GDC (molar), 32 % Zn (molar) and 24 % Ni

(molar) has a 40 times higher conductivity than NKSDC electrolyte.

It has also been observed that the conductivity increases with the increase of

temperature which shows that this anode does not possess metallic characteristics.The

conductivity value of Dry-7 in atmosphere is 1.77 S/cm at 600oC. If a material is to be

used as a cathode it requiresbeing a conductivity of ≥ 1 S/cm under air atmosphere.

Therefore, it can also be used as cathode material. According to conductivities results,

this anode has dual characteristics, one is electronic and second is oxygen conductor.

300 350 400 450 500 550 600

0

1

2

3

4

5

Co

nd

ucti

vit

y (

S/c

m)

Temperature (oC)

DC Conductivities at Hydrogen Atmosphere

Dry1 Dry3 Dry5 Dry7 Dry9

Figure 5.3: DC Conductivities of Dry 1-9 (Odd Compositions) at H2 Atmosphere


92

300 350 400 450 500 550 600

0.0

0.4

0.8

1.2

1.6

2.0DC Conductivities at AIR Atmosphere

Con

du

cti

vit

y (

S/c

m)

Temperature (oC)

Dry1 Dry3 Dry5 Dry7 Dry9

Figure 5.4: DC Conductivities of Dry 1-9 (Odd Compositions) at Air Atmosphere

5.1.5 Performance Measurements

A sodium-potassium carbonated samarium doped ceria NKSDC electrolyte

and BSCF cathode were used to complete the fuel cell. The detailed scheme to

complete the cell of each composition has been illustrated in Table 4.16. The

performance of each composition based on CNZGC anode at 550oC is shown in

Figure 5.5. Unfilled symbols show Current Density VS Voltage and filled symbols

show Current Density VS Power Density in the Figure 5.5.

Hydrogen was fed as fuel at anode side and air as oxidant at cathode side.

Open circuit voltage OCV was recorded to be 0.825V, 0.7V, 0.53V, 1.025V and 1.0V

for Dry-1, Dry-3, Dry-5, Dry-7 and Dry-9 composition respectively. The power

density from the I-V curve was calculated as 477, 256, 110, 570 and 554mW/cm2. It

has been found that the composition Dry-7 has the maximum power density. It was

observed that 31% addition of GDC in one step anode/electrode preparation provides


93

better results. However, all values of GDC other than 31% (molar) show less power

densities.

0 400 800 1200 1600 20000.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

0

100

200

300

400

500

600

700

800

←

Pow

er D

en

sity

(m

W/c

m2)

Volt

age (

V)

Current Density (mA/cm2)

Dry-1 Dry-3 Dry-5 Dry-7 Dry-9

←

Figure 5.5: Performance of Dry 1-9 (Odd Compositions) at 550oC.

Table 5.2: Conductivity, Activation Energy and Performance Data of CNZGC

Sample Category

Temp. (oC)

DC Conductivity (S/cm)

Activation Energy (eV)

at H2 Atmosphere

Max. OCV (V)

Maximum Power Density

(mW/cm2) At H2 At AIR

Dry-1 550 0.23 0.20 0.32 0.825 478

Dry-3 550 0.29 0.11 0.35 0.7 256

Dry-5 550 0.11 0.09 0.16 0.53 108

Dry-7 550 4.14 1.76 0.04 1.025 570

Dry-9 550 0.12 0.10 0.23 1 554


Arrhenius plot of Dry 1-9 (odd compositions) is shown in Figure 5.6 and

activation energy of all compositions was calculated by linear fitting technique using


94

Origin 7.0 software and listed in Table 5.2. It has been observed that Dry-7

composition has minimum activation energy of 0.04eV as shown in Figure 5.7. A

very low value of the activation energy implies that the chemical reaction in the fuel

cell starts immediately.

1.1 1.2 1.3 1.4 1.5

3.0

3.5

4.0

4.5

5.0

5.5

6.0

6.5

7.0

7.5ln

σΤ

σ

Τ

σΤ

σ

Τ (

S/c

m.K

)

Arrhenius Plot of Dry 1-9 (odd Composition ) at Hydrogen Atmosphere

1000/T (K-1)

Dry-1 Dry-3 Dry-5 Dry-7 Dry-9

Figure 5.6: Arrhenius Plots of Dry 1-9 (Odd Compositions) at H2 Atmosphere

1.10 1.15 1.20 1.25 1.30 1.35 1.40 1.45 1.50

6.2

6.4

6.6

6.8

7.0

7.2

7.4

1000/T (K-1)

ln σ

Τσ

Τσ

Τσ

Τ (

S/c

m.K

)

Arrhenius Plot of Dry-7

1.1 1.2 1.3 1.4 1.5 1.6

5.8

6.0

6.2

6.4

6.6

6.8

7.0

7.2

7.4

7.6

ln σ

Τσ

Τσ

Τσ

Τ(S

/cm

)

1000/T (K-1)

Linear Fit of Dry-7

Linear Fit

Ea = 4x10 -2

eV

Figure 5.7: Arrhenius Plot and its Corresponding Linear Fit Curve (Inset)

Calculation of Activation Energy of Sample Dry-7


95

5.1.7 XRD Patterns and Performance of Dry-7 Sintered at Various

Temperatures

After finding out the fact that the Dry-7 composition, sintered at 800oC for

four hours, yields maximum power density at 550oC. The Dry-7 sample was prepared

a fresh and studied its performance after sintering it at 700, 800, 900 and 1000oC for

four hours. The purpose was to check if sintering at other temperature could yield

better results. XRD patterns were also recorded of this sample after each sintering. It

was noted that the structure found at 700oC remains intact even at 1000oC as same as

shown in figure 5.8. All the peaks were indexed and the structure was found to be

three phases. However, it has been viewed that a 700oC temperature is enough to

create nanostructures, but the performance was not so high at this sintering

temperature. The particle size of Dry-7 composition was also calculated at different

sintering temperature and results are shown in Table 5.3.

Figure 5.9 shows the fuel cell performance of composition Dry-7 sintered at

various temperatures. It has been found that sintering at 700oC gives very low

performance while Dry-7 sintered at 800oC and 1000oC has almost equal power

densities. The challenge is to reduce the temperature. We found that the optimized

sintering temperature is 800oC, which creates nanostructures and provides high

performance.

Table No.5.3: Average Particle Size Data of Dry-7 Compositions

Sample Category Sintering Temperature (oC) Average Particle Size (nm)

Dry-7 700 37.06

Dry-7 800 20.69

Dry-7 900 20.46

Dry-7 1000 21.02


96

Figure 5.8: XRD patterns of Composition Dry-7 at Various Sintering Temperatures

0 400 800 1200 1600 2000 2400

0.2

0.4

0.6

0.8

1.0

1.2

0

100

200

300

400

500

600

Pow

er D

ensi

ty (

mW

/cm

2)

Volt

age (

V)


T700oC (Sintering) T800oC (Sintering) T900oC (Sintering)

T1000oC (Sintering)

Performance Temperature 550 oC

←

←

Figure 5.9:Performance of Dry-7 at 550oC (Sintered at 700, 800, 900and 1000oC)

0

4000[NZGDC-700oC.ASC] 10.008 225

0

4000[NZGDC-800oC.ASC] 10.008 267

0

4000[NZGDC-900oC.ASC] 10.008 240

0

4000[NZGDC-1000oC.ASC] 10.008 236

65-9470> NiZn - Nickel Zinc

44-1159> NiO - Nickel Oxide

43-1014> Gd2O3 - Gadolinium Oxide

65-7999> Ce4O7 - Cerium Oxide

20 30 40 50 60 70

2-Theta(°)

Inte

ns

ity(C

ou

nts

)


97

5.1.8 Cost Analysis

The estimated cost of the CNZGC named as Dry-7 electrode material has been

calculated and shown in Table 5.4:

Table 5.4:Estimated Cost of Dry-7 Electrode (Cu0.13Ni0.24Zn0.32Gd0.12Ce0.19) CNZGC

Item Weight (gram) € PKR

CuCO3Cu(OH)2 8.75 1.53 200 NiCO3 9.10 1.18 153.32 Zn(NO3)2.6H2O 37.70 3.31 429.00 Gd(NO3)3.6H2O 17.30 103.45 13408.52 Gd(NO3)3.6H2O 27.30 8.66 10887.20 CNZGC Total Cost / 100g 118.15 15313.50 Sintering Present Charges 10 Commercial Units 2.00 260 Labor Cost Researcher per day Salary 8.00 1050 Others Any extra 1.18 153.56 Total Cost After sintering G. T / 40 gm 130 16850

5.1.9 CONCLUSIONS

Different compositions of CNZGC were synthesized by dry method and their

structural properties, conductivities and performance were studied. The sintering

at800oC produced crystalline and nanostructure powders. Their conductivities were

investigated by dc technique at hydrogen and air atmosphere. It is concluded that Dry-

7 composition has a maximum electrical conductivity of 4.14 S/cm at 550oC which

can fulfill the requirements of an electrode/anode. The maximum OCV, current

density and power density was also determined as 1.025V, 1875mA/cm2 and

570mW/cm2 respectively for this composition. It has also been concluded that the

optimized composition Dry-7 (studied and analyzed from all aspects, sintering

temperature, structure characterization, conductivity, activation energy , OCV and

power density) is very suitable for nanocomposite electrode/anode in advanced low

temperature solid oxide fuel cell LTSOFC (300-600oC) applications. The estimated

cost has been calculated as 32.50€/10gm, which is more than 50% cheap than that of

conventional electrode NiO commercially available in powder form at Sigma Aldrich.


98

5.2 Sample No. 2 (a-e) ---------- Al0.1NixZn0.9-x (ANZ)

5.2.1 Introduction

This anode sample consists of Al0.1NixZn0.9-x composition. These

compositions were prepared by solid state reaction method and named as 44(a), 44(b),

44(c), 44(d) and 44(e). These five samples were prepared in order to optimize the

molar percentage of Zn element with less Ni element keeping Aluminum (Al) molar

ratio constant in all compositions. The aim of this study and work is to reduce the Ni

contents in anode materials by replacing it with Zn element, which can work at

comparatively low temperature range (400-550oC). The detailed study and analysis of

the anode material and its behavior with different Zn ratios is extensively discussed

below.

5.2.2 Structural Studies

Figure 5.10 shows the crystallographic structure of the compositions

Al0.1NixZn0.9-x where x= 0.1, 0.2, 0.3, 0.4 and 0.5. The results exhibit that all the

samples which were sintered at 800oC for four hours has a crystalline structure. The

small amount of Al in the material has been completely doped in Ni-Zn components,

because XRD patterns when analyzed in detail by MDI-Jade 5 software doesn’t show

any peak of the Al content. Average Particle sizes of all compositions were calculated

using Scherer’s equation from the XRD peaks of Al0.1NixZn0.9-x and shown in Table

5.5.The values of average particle size as worked out from different peaks of XRD

pattern were found to be in the range of 24-51 nm, which revealed that the sintering at

800oC creates good nanostructure crystallites.


99

30 40 50 60 70 80 90

2000

4000

6000

8000

10000

12000

14000

16000

♥♥♥♥♣♣♣♣

♥♥♥♥♥♥♥♥

♥♥♥♥

♥♥♥♥

♣♣♣♣

♣♣♣♣

♣♣♣♣

♣♣♣♣♣♣♣♣♣♣♣♣♣♣♣♣

Inte

nsi

ty (

a.u

)

2θθθθ

44(a) 44(b) 44(c) 44(d) 44(e)

♣♣♣♣ZnO

♥♥♥♥NiO♣♣♣♣

♥♥♥♥

x44a

=0.1

x44b

= 0.2

x44c

= 0.3

x44d

= 0.4

x44e

= 0.5

Figure 5.10: XRD Patterns of Different Composition of Al0.1NixZn0.9-x, (x = 0.1 – 0.5)

Composite anode material was prepared by mixing 20wt. % of gadolinium

doped ceria (GDC) electrolyte into Al0.1Ni0.2Zn0.7 [44(b)]. The selection of 44(b) is

based on its performance as anode (see Figure 5.20). The XRD patterns of the

composite anode ANZ-GDC were recorded and are shown in Figure 5.11. A close

look of XRD pattern (Figure 5.11) indicates that it contains peaks corresponding to Ni

and Zn only whereas no peak exists for GDC. This implies that GDC is completely

doped into ANZ anode.


100

Figure 5.11: XRD Pattern of Composition A0.10N0.20Z0.70-GDC Composite Anode

5.2.3 Microstructure View (Scanning Electron Microscopy) SEM

Figure 5.12 shows the microstructure of the optimized composite anode of

sample 44(b) Al0.1Ni0.2Zn0.7. It has been found from SEM image that particles are in

the range of 20-50 nm. These results are comparable to those obtained from XRD

data, which further confirms that the present material possesses nanostructure.

According to SEM photograph, it can be observed that the ANZ-GDC composite

anode is well homogeneous and has a porosity to transfer the ions coming from the

cathode side during the cell reaction.


101

Figure 5.12:Scanning Electron Microscopic Image of Composite Al0.1Ni0.3Zn0.6-GDC


Both DC and AC conductivities of each sample were measured at hydrogen

atmosphere in the temperature range of 300-600oC and their results are shown in

Figure 5.13 and 5.14, and listed in Table 5.5. The value of DC conductivity was found

to be 10.11 S/cm and that for AC conductivity was 4.94 S/cm of sample 44(b) at

hydrogen atmosphere. The conductivity value of GDC electrolyte is reported to be 0.1

S/cm [8]. This means that the DC conductivity of ANZ is more than 100 times greater

than that of the electrolyte (GDC) used in the present work. This is in agreement with

the generally accepted standard which requires that the anode material should have its

conductivity at least 10 times greater than the electrolyte [9-10]. All the other samples

have lower conductivities than that of 44(b).


102

300 350 400 450 500 550 6000

1

2

3

4

5

6

7

8

9

10

11

12

Con

du

cti

vit

y (

S/c

m)

Temperature (oC)

44(a) 44(b) 44(c) 44(d) 44(e)

DC Conductivity of Al0.1

NixZn

0.9-x at H

2 Atmosphere

Figure 5.13: DC Conductivity of Al0.1NixZn0.9-x Anode at Hydrogen Atmosphere

350 400 450 500 550 6000.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

5.0

5.5

6.0

Con

du

cti

vit

y (

S/c

m)

Temperature (oC)

44(a) 44(b) 44(c) 44(d) 44(e)

AC Conductivity of Al0.1

NixZn

0.9-x at H

2 Atmosphere

Figure 5.14: AC Conductivities of Al0.1NixZn0.9-x Anode at Hydrogen Atmosphere


103


In order to calculate the activation energy of each sample at hydrogen

atmosphere, Arrhenius curve has been plotted and shown in figure 5.15 and 5.16.

Using the linear fit technique, the activation energy was calculated with the help of

formula

exp

Where σ is the conductivity, T is temperature in kelvin, A is exponentional factor and

k is Boltzmann’s constant. The results of activation energies of all samples are listed

in Table 5.5. The results of measurements of activation energy for sample 44(b) are

shown in Figure 5.17 and 5.18. The activation energy of the sample 44(b) was found

to be 2.7x10-2 and 9.6x10-2 from DC and AC data, respectively.

Table 5.5: Conductivity, Activation Energy and Particle Size Data of ANZ

Sample Category

Temp.(oC) Conductivity at H2 Atmosphere

(S/cm)

Activation Energy (Ea) (eV)from Conductivity

of

Particle Size (nm)

DC AC DC AC

44(a) 600 2.79 1.39 5.9x10-2 7.3x10-2 34.55

44(b) 600 10.84 4.88 2.7x10-2 9.6x10-2 50.21

44(c ) 600 0.90 0.96 4.9x10-2 7.6x10-2 24.70

44(d) 600 1.31 1.54 4.4x10-2 8.3x10-2 24.57

44(e) 600 0.79 0.85 3.1x10-2 8.0x10-2 31.10


104

1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.85.6

6.0

6.4

6.8

7.2

7.6

8.0

8.4

8.8

9.2

9.6

ln σσ σσ

T (

S/c

m.K

)

1000/T (k-1)

44(a) 44(b) 44(c) 44(d) 44(e)

Figure 5.15: Arrhenius Plots of DC Conductivities of Al0.1NixZn0.9-x at H2atm.

1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8

6.0

6.4

6.8

7.2

7.6

8.0

8.4

8.8

9.2

ln σσ σσ

T (

S/c

m.K

)

1000/T (K-1)

44(a) 44(b) 44(c) 44(d) 44(e)

Figure 5.16: Arrhenius Plots of AC conductivities of Al0.1NixZn0.9-x at H2atm.


105

1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.88.6

8.7

8.8

8.9

9.0

9.1

1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.98.5

8.6

8.7

8.8

8.9

9.0

9.1

9.2

lnσσ σσ

T (

S/c

m.K

)

1000/T (k-1)

Linear Fit of Sample 44(b)

Ea = 2.7x10 -2

eV

Linear Fit

Linear Fit Data from DC Conductivity at H

2 Atmopshere of Sample 44(b)

lnσσ σσ

T (

S/c

m.K

)

1000/T (k-1)

Figure 5.17: Linear Fit Curve of Sample 44(b) for Activation Energy from

DC Conductivity at Hydrogen Atmosphere

1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8

8.4

8.5

8.6

8.7

8.8

8.9

9.0

9.1

9.2

1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9

8.4

8.6

8.8

9.0

9.2

ln σσ σσ

T (S/c

m.K

)

Temperature (K-1)

Linear Fit Data

Ea = 9.6x10-2

Linear Fit

ln σσ σσ

T (

S/c

m.K

)

1000/T (K-1)

Linear Fit Data from AC Conductivityat H

2 Atmosphere from Sample 44(b)

Figure 5.18: Linear Fit Curve of Sample 44(b) for Activation Energy from AC Conductivity at Hydrogen Atmosphere


106

5.2.6 AC Electrochemical Impedance Spectroscopy (EIS) Analysis

The anode performance of composite anode 80 wt. %ANZ-20 wt. % GDC was

also investigated by AC Electrochemical Impedance Spectroscopy at hydrogen

atmosphere. The results shown in Figure 5.19 indicate that at all temperatures except

550oC; the samples have almost same response. The experimental curves of

impedance spectra correspond to a pure electronic behavior at all temperatures [11].

The impedance spectra of 80 wt. % ANZ-20 wt. % GDC anode at low frequency

intercept give high resistance due to addition of electrolyte. However, resistance

becomes low at high-frequency intercept.It has been reported [12] in previous work

that the composition of 20wt. % electrolyte and 80wt. % anode is the most compatible

composition, which provides a good electronic conductivity and facilitates the

transportation of ions through electrolyte.

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9-0.5

0.0

0.5

1.0

1.5

2.0

2.5

3.0

Zim

(O

hm

)

Zre

(Ohm)

T 550oCT 500oC

T 450oC

T 400oC T 350oC

AC Impedance Spectra of80%ANZ-20%GDC at H

2 Atmosphere

Figure 5.19: AC Electrochemical Impeadance Sepctra at Different Temperatures.


107


The performance of all the anode samples using GDC as electrolyte and BSCF

as cathode were measured. It has been found that the sample named as 44(b), having

70 % Zn, exhibits a maximum performance, whereas all other Zn percentage values

yield low performance. For all samples [44(a), 44(b), 44(c), 44(d) and 44(e)], the

maximum OCV values were found to be 0.965, 1.030, 0.908, 0.875 and 0.760 V at

550oC, respectively. I-V curves were drawn from the data. From the I-V results,

power density was also calculated and I-P curves were drawn and shown in Figure

5.20. In this figure, unfilled emblems show the current density versus power density

and solid emblems correspond to current density versus voltage. The complete data of

OCVs, current densities and power densities are tabulated in Table 5.6.

0 300 600 900 1200 1500 18000.0

0.2

0.4

0.6

0.8

1.0

1.2

0

100

200

300

400

500

600

700

800

Pow

er

Den

sity

(m

W/c

m2)

Volt

age

(V)

Current Desity (mA/cm2)

44(a) 44(b) 44(c) 44(d) 44(e)

Performace Temperature = 550oC

←←

Figure 5.20: Performance Measurements of Samples 44(a), 44(b), 44(c), 44(d) and

44(e)


108

Table 5.6: Performance Data of ANZ-GDC Composite Anodes

Cell Category

Temp. (oC)

Maximum OCV (V)

Maximum Current Density

(mA/cm2)

Maximum Power Density

(mW/cm2)

44(a) 550 0.965 991.25 303.28

44(b) 550 1.030 1725 705.56

44(c ) 550 0.908 503.12 139.5

44(d) 550 0.875 1003.12 296.48

44(e) 550 0.760 801.56 171.94

5.2.8 Cost Analysis

The estimated cost of ANZ electrode has been calculated including raw

materials, Power cost, researcher’s salary and other. It has been found that the present

prepared electrode for solid oxide fuel cell is cheaper than those of used in

conventional Ni based electrode; for example NiO electrode in powder form is

available commercially from chemical supplier Sigma Aldrich and its cost is

127.08€/20 gram. The ANZ named as 449b) electrode/anode reported in this research

work has an estimated cost of 35€/20 gram. The calculation of cost has been

illustrated in Table 5.7:

Table 5.7: Estimated Cost of 44(b) Electrode (Al0.1Ni0.2Zn0.7) ANZ Item Weight (gram) € PKR

Al(NO3)3.9H2O 13.05 51.48 6672.53

NiCO3 4.15 0.54 70.00

Zn(NO3)2.6H2O 82.80 7.27 942.23

ANZ Total Cost / 100g 59.30 7685.02

Sintering Present Charges 10 Commercial Units 2.00 260.00

Labor Cost Researcher per day Salary 8.00 1050.00

Others Any extra 0.70 153.56

Total Cost After sintering G. T / 40 gram 70.00 9072.60


109

5.2.9 CONCLUSIONS

The anode materials ANZ (different compositions)and composite anode

(ANZ-GDC) have been successfully synthesized by solid state reaction method. XRD

patterns indicate that all compositions have their particle sizes in the range of 20-

50nm. It has been observed that the composition 44(b) having 70% Zn element has

maximum power density of 705mW/cm2 in the temperature range of 400-550oC. It

has also been observed that this composition also has maximum conductivity and

minimum activation energy. The sample 44(b) provides maximum performance.

These Zn based anodes with fewer contents of Ni show stable performance as well as

conductivity. The purpose of this study was to find the composite anodes on the basis

of NANOCOFC approach, which is very good for the commercialization of the

SOFC. All the samples were analyzed and tested with all aspects and it has been

concluded that the sample 44(b) is highly suitable as far as conductivity and

performance is concerned. This sample can help to find out the new anode materials

for low temperature solid oxide fuel cell.


110

5.3 Sample No. 3 ---------- Cu0.2Mn0.2Zn0.6 (CMZ)

5.3.1 Introduction

The sample No. 3 consists of Cu0.2Mn0.2Zn0.6 (CMZ) electrode material. This

material was successfully synthesized by solid state reaction method. The prepared

Sodium Carbonated Samarium Doped Ceria NSDC electrolyte was added with CNZ

anode material in different weight ratio such as 0 %, 10 %, 20 %, 30 %, and 40 %.

The main objective was to find out the compatibility of electrode and electrolyte ratio,

which could give better performance. The compatibility of anode and electrolyte was

also studied by AC Electrochemical Impedance Spectroscopy analysis. However,

structure analysis, particle size, electrical conductivity, AC Impedance, and

performance are discussed below in detail:

5.3.2 XRD Patterns

Figure 5.21 shows the XRD pattern of CMZ electrode material with

appropriate composition of Cu0.2Mn0.2Zn0.6. The XRD resultsindicate that the mixed

Cu0.2 Mn0.2 Zn0.6 O1.9 anode material is well crystallized and contains all the elements

used in its preparation. The long peak corresponds to ZnO while others peaks

represent CuO and MnO. The particle size was calculated from XRD pattern of the

powder by using Scherer’s formula and listed in Table 5.8. It has been observed that

sintering at 800oC creates nanostructure showing a particle size of 31.50nm.


111

Figure 5.21: XRD Pattern of Cu0.2Mn0.2Zn0.6 Electrode Sintered at 800oC

5.3.3 SEM Analysis

Figure 5.22 shows the homogeneity of the mixed powder and has a fine

grained microstructure. The microstructure of sintered Cu0.2Mn0.2Zn0.6 is relatively

promising porous structure. SEM photograph of Cu0.2Mn0.2Zn0.6 anode material

indicates nano sized particles which supports XRD results of this material.

Figure 5.22: SEM Image of Cu0.2Mn0.2Zn0.6 Electrode


112


The dc conductivity was measured both at hydrogen and air atmosphere in the

temperature range of 300-600oC. The measurements are represented in figure 5.23,

which show that dc conductivity of the mixed conductor measured under hydrogen

atmosphere is greater than the conductivity measured at air atmosphere. The electrical

conductivity was found to be 6.37 S/cm and 3.79 S/cm at hydrogen and air

atmosphere, respectively. It has been reported in literature [13] that the electronic

conductivity should be at least 10 times higher than the ionic one.This mixed

electrode shows 60 and 30 times greater electronic conductivity than the ionic

conductivity of the used electrolyte NSDC. This NSDC electrolyte has standard ionic

conductivity 0.1S/cm at a temperature of 600oC [13]. As, it shows a reliable

conductivity, therefore it can be used as either anode or cathode material in order to

measure its performance for solid oxide fuel cell.For this reason, the

Cu0.20Mn0.20Zn0.60 material has been used as anode as well as cathode in the present

work.


113

350 400 450 500 550 600 6501

2

3

4

5

6

7

CuMnZn Electrode Conductivity at H2 Atmosphere

CuMnZn Electrode Conductivity at Air Atmosphere

Con

du

cti

vit

y (

S/c

m)

Temperature (oC)

Figure 5.23: DC Conductivities of Electrode at Hydrogen and Air Atmosphere


The activation energy of the electrode material was calculated from dc

conductivity data by using Arrhenius plots shown in Figure 5.24 and 5.25.

The activation energy of pure electrode was found to be 0.060eV and 0.075eV at

hydrogen and air atmosphere, respectively. The calculated activation energy has been

listed in Table 5.8. These results exhibit that the mixed electrode requiresa very little

time to start the reaction, which emphasizes that as soon as fuel is supplied, the

chemical reaction starts.


114

Figure 5.24: Arrhenius Plot of DC Conductivity at Hydrogen Atmosphere

1.20 1.25 1.30 1.35 1.40 1.45 1.507.45

7.50

7.55

7.60

7.65

7.70

7.75

ln σσ σσ

T (

S/c

m.K

)

1000/T (K-1)

1.15 1.20 1.25 1.30 1.35 1.40 1.45 1.50 1.557.40

7.45

7.50

7.55

7.60

7.65

7.70

7.75

Linear Fit

Ea = 7.4910-2

ln σσ σσ

T (S/c

m.K

)

Temperature (K-1)

Linear Fit Data

Arrhenius Plot of DC Conductivity at AIR Atmosphere

Figure 5.25: Arrhenius Plot of DC Conductivity at Air Atmosphere

1.20 1.25 1.30 1.35 1.40 1.45 1.50

8.25

8.30

8.35

8.40

8.45

8.50

1.15 1.20 1.25 1.30 1.35 1.40 1.45 1.50 1.558.20

8.25

8.30

8.35

8.40

8.45

8.50

ln T

σσ σσ(S

/cm

.K)

1000/T (K-1)

Ea = 6.00 x 10- -2

Linear Fit

Linear Fit Data

ln T

σσ σσ(S

/cm

.K)

1000/T (K-1)

Arrhenius Plot of DC Conductivity at H2 Atmosphere


115

Table 5.8: Particle Size, ASR, Conductivity, Activation Energy and Performance

Sample Category

Particle Size (nm)

DC Conductivity at Atmosphere (S/cm)


Max. Power Density

(mW/cm2) H2 AIR H2 AIR

CMZ 31.50 5.789 2.73 6.0x10-2 7.5x10-2 728.86

5.3.6 AC Electrochemical Impedance Spectroscopy (EIS)

The impedance spectra of Cu0.20Mn0.20Zn0.60 containing 0, 20, 30 and 40

weight % of NSDC electrolyte compositions were recorded at 500oC. The results of

measurements are shown in Figure 5.26. Experimental curves show that the pure

electrode having no NSDC electrolyte did not yield any thing except square dots in

the impedance plots. The absence of any curves tells that the conductivity is purely

electronic in nature [14]. The results corresponding to different amounts of

electrolytes produced curves which represent a mixed conductivity due to electrons

and ions. These spectra of different electrolytic ratio also show that the conductivity

of the material decreases with the increasing amount of electrolyte. The impedance

spectrum of mixed electrolyte at high-frequency intercept gives the low resistance of

the electrode but resistance becomes high at low-frequency due to the addition of the

electrolyte, the current collectors and the lead wires.It is evident from the figure that

mixed electrode having 20 wt% of NSDC electrolyte and 80 wt% of CMZ electrode

showed the best results in terms of conductivity and performance (Figure 5.27 and

5.28). However, an increase in the NSDC content upto 30 wt. % or 40 wt. % resulted

in a decrease of the conductivity and performance. Each spectrum was simulated by

ZSim Win software and equivalent circuit was drawn. The equivalent circuit LR(QR)

gives the inductance (L), resistance (R) for electrolyte and Q for constant phase

element.


116

0 5 10 15 20 25 30 35 40

-14

-12

-10

-8

-6

-4

-2

0

2

4

Zim

(Oh

m)

Zre

(Ohm)

Experimental Pure CuMnZn Simulated Pure CuMnZn Experimental 80/20 Ratio Simulated 80/20 Ratio Experimental 70/30 Raio Simulated 70/30 Ratio Experimental 60/40 Ratio Simulated 60/40 Ratio

Figure 5.26: Comparisons of AC Impedance Spectra of Different Ratios of Electrode to

Electrolyte (wt. %age of Electrode to Electrolyte)

5.3.7 Conductivities of Mixed Electrodes

The conductivities of mixed electrodes samples with different wt. % of NSDC

electrolyte and CMZ electrode were measured at 550oC using KD-2531 China. The

results are shown in Figure 5.27 and listed in Table 5.9. This figure indicates that the

composite electrode was becoming more ionic conductor in character as the NSDC

content was increased. It also lowered the conductivity of the electrode. The mixed

electrode composition (80 wt. % CMZ and 20 wt. % NSDC) depicted the best

conductivity which makes it a suitable candidate for LTSOFC.


117

0 10 20 30 400.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

5.0

5.5

6.0

Condactivity with different % age ratio of NSD Electrolyt in CuMnZn Electrode at Hydrogen Atmosphere

Con

du

ctiv

ity (

S/c

m)

wt %age of NSDC Electolyte in CMZ electrode

Figure 5.27: Conductivity of CMZ Electrode Containing Different wt. % of NSDC

Electrolyte Measured at 550oC

5.3.8 Performance of Mixed Electrodes

The performance of mixed electrodes samples with different wt. % of NSDC

electrolyte and CMZ electrode were measured at 550oC using fuel cell testing unit L-

43 China. The performance measurements are shown in Figure 5.28. The maximum

OCV of each ratio was found to be 0.872, 0.990, 1.124, 0.89 and 0.775 respectively.

The current density and power density have a maximum value of 2031.25mA/cm2 and

728.86mW/cm2, respectively. The values of these quantities of all compositions are

listed in Table 5.9. The performance of this ratio was also measured in a temperature

range of 400-550oC. The open circuit voltage was recorded to be 1.124, 1 V, 0.850V

and 0.940V at 550oC, 500oC, 450oC and 400oC, respectively, and The I-V and I-P

characteristics were drawn in Figure 5.29.


118

0 500 1000 1500 20000.0

0.2

0.4

0.6

0.8

1.0

1.2

-100

0

100

200

300

400

500

600

700

800←

Pow

er D

ensi

ty (

mW

/cm

2)

Volt

age

(V)


100:0 90:10 80:20 70:30 60:40

Operating Temperature = 550oC

←

Figure 5.28: Performance of CMZ Electrode Containing Different wt. % of NSDC

Electrolyte Measured at 550oC

0 500 1000 1500 2000 25000.0

0.2

0.4

0.6

0.8

1.0

1.2

-100

0

100

200

300

400

500

600

700

800

Pow

er D

en

sity

(m

W/c

m2)

Volt

age (

V)


T550oC

T500oC T450oC

T400oC

← ←

Figure 5.29: Fuel Cell Performance of Electrode Having 80 wt. % CMZ and 20 wt.

% NSDC over a Temperature Range of 400-550oC


119

Table 5.9: Conductivity and Performance Data of CMZ100-x-NSDCx Anode

Sample Category %age value of x

Temp.(o C) Conductivity in H2

(S/cm)

OCVs (V)

Max. Current Density

(mA/cm2)

Max. Power Density

(mW/cm2)

0 550 5.79 0.872 480 132.6

10 550 0.85 0.990 1312.5 448.12

20 550 2.35 1.124 2031.25 728.86

30 550 0.78 0.890 868.75 266.65

40 550 0.52 0.775 750.65 146.39

5.3.9 Cost Analysis

Table 5.10 indicates the ground cost of CuMnZn material having 60% molar

ratio of Zn. The prepared powder has used as electrode material in solid oxide fuel

cell. This is the Ni free electrode material which possesses all the basic requirements

for solid oxide fuel cell. However, the compatibility of anode with electrolyte or

cathode material is also a significant factor to enhance the cell performance. The

further study has been extended to elucidate supporting cheap compounds to enhance

the cell performance and has been discussed in next section. The cost of CMZ

electrode is estimated as 42€/20 grams. The calculation is as following;

Table 5.10: Estimated Cost of (Cu0.2Mn0.2Zn0.6) CMZ Electrode


CuCO3.Cu(OH)2 14 2.478 321.17

Mn(NO3)2 16 63.12 8180.89

Zn(NO3)2.6H2O 70 6.146 798.57

CMZ Total Cost / 100g 71.744 9300.00






120

5.3.10 CONCLUSIONS

Cu0.2 Mn0.2 Zn0.6 O1.9electrode was successfully synthesized by solid state

reaction method and its electrochemical properties were studied. This mixed electrode

has the following conclusive aspects.

Cu0.2Mn0.2Zn0.6 possesses nanostructure of 31.50 nm.

This material executes electronic conduction behavior dominantly.

The CuMnZn material exhibits conductivity of 2.73 S/cm at air atmosphere,

which can make its use very fruitful as cathode material for SOFC.

The 80 wt. % CMZ and 20 wt. % NSDC composition is a suitable composition

for performance as well as conductivity measurements.

AC impedance spectra of this composition indicate electronic and ionic

behavior, which can construct the best high way to transport the ions.

These measurements support the idea that the material is a suitable candidate as an

electrode for low temperature solid oxide fuel cell.

Chapter No.5 Results and Discussion Sample No.4

121

5.4 Sample No. 4 (a-f) ---------- Ba0.05Cu0.25FexZn0.7-x (BCFZ)

5.4.1 Introduction

The sample No. 4 consisted of Ba0.05Cu0.25FexZn0.7-x (BCFZ) electrode/anode

material. For conductivity measurement, the pure BCFZ electrode was tested and for

performance test, 20wt.% NKCDC electrolytes was added with BCFZ to make it

composite anode (80wt.% BCFZ and20wt.% NKCDC). A symmetrical cell of BCFZ-

NKCDC composite electrode was tested. Among all the compositions, only one

composition (BCFZ-5) exhibiteda high performance. This BCFZ-5 material was also

tested using BSCF cathode as in asymmetrical fuel cell configuration. The

characterization and electrochemical study of BCFZ material has been discussed in

detail:

5.4.2 Crystallographic Analysis

The XRD patterns were recorded for all compositions of Ba0.05Cu0.25FexZn0.7-x

electrode/anode material, where x = 0, 0.02, 0.04, 0.06, 0.08, 0.10 and 0.12. The

results are shown in Figure 5.30. The XRD patterns indicate that in the absence of Fe,

the structure is not well defined; however, the addition of iron into the material

changes the structure. These XRD patterns show the structure is single phase having

only Zn element by shifting Fe and Cu peaks into Zn during the sintering process. No

other peaks of barium, copper and iron were found in XRD pattern. The peaks were

indexed and structure was found to be hexagonal. The average crystalline size of all

the samples were calculated by applying Scherer’s formula and found in the range of

20-80nm.

Figure 5.31 shows the X-Ray diffractometery of the prepared BCFZ-5 anode,

BSCF cathode and NKCDC electrolyte. Indexing of all the peaks in XRD pattern of


122

NKCDC reveals that the NKCDC electrolyte possesses cubic fluorite structure [15].

No individual phase of calcium was found; hence the calcium has been doped

completely into ceria described in our reported work [15]. BSCF cathode has

pervoskite structure as discussed in detail [16]. It has been found that BCFZ anode is

electrochemically compatible with NKCDC electrolyte. Both the materials BCFZ-5

and NKCDC have single phase structure and both have nano size particles as

indicated by the XRD and SEM results.

20 40 60 80 100

0

5000

10000

15000

20000

25000

30000

35000

40000

♣♣♣♣♣♣♣♣♣♣♣♣♣♣♣♣

♣♣♣♣♣♣♣♣

♣♣♣♣ ♣♣♣♣ ZnO

x = 0.12

x = 0.10

x = 0.08

x = 0.06

x = 0.04

x = 0.02

x = 0

Inte

nsi

ty (

a.u

)

2 θθθθ

Figure 5.30: Crystallographic View of Ba0.05Cu0.25FexZn0.70-x Anode, Where x = 0, 0.02, 0.04, 0.06, 0.08, 0.10 and 0.12 mol %.


123

0 10 20 30 40 50 60 70 80 90

0

3000

6000

9000

12000

15000

18000

⊕⊕⊕⊕⊕⊕⊕⊕

⊗⊗⊗⊗⊗⊗⊗⊗

⊗⊗⊗⊗

⊕⊕⊕⊕

♣♣♣♣

♣♣♣♣

♣♣♣♣ ♣♣♣♣♣♣♣♣

♣♣♣♣♣♣♣♣

♣♣♣♣

Inte

nsi

ty (

a.u

)

2θθθθ

♣♣♣♣ ZnO

⊗⊗⊗⊗ CeO

BCFZ

BSCF

NKCDC

⊕⊕⊕⊕ CoFe

Figure 5.31: X-Ray Diffraction Patterns of BCFZ-5, Anode, BSCF Cathode and

NKCDC Electrolyte Materials.

5.4.3 Scanning Electron Microscopy (SEM)

Figure 5.32 shows the surface morphology of the BCFZ-5 electrode/anode

materials. The particles of different sizes of 20-80 nm are found from SEM image. It

can be clearly observed from SEM micrograph that there are many pores in the

material.

Figure 5.32: SEM Micrograph of BCFZ-5 Anode Material


124

5.4.4 Electrical Conductivity Measurements

The electrical conductivities of all the samples (BCFZ-1 to BCFZ-6) were

measured at hydrogen atmosphere by using Digital Micro-ohm meter KD-2531

China. The results are shown in Figure 5.33 and listed in Table 5.11. The results

depicted that the conductivity of the materials is increasing gradually with the

increase of iron content. The BCFZ-5 composition having 1 mol % of iron possesses

the highest conductivity of 25.84 S/cm at 600oC in hydrogen atmosphere. This

conductivity value is the highest of all the samples. However, the increment of iron

other than 1 mol % into the composition causes to lower the conductivity.

The electrical conductivity of this material was also measured at air atmosphere to see

if it could be used as a possible cathode. The results are shown in Figure 5.34 and

listed in Table 5.11. It can be seen from graph that at air atmosphere, three

compositions (BCFZ-3, BCFZ-4 and BCFZ-5) have their conductivities greater than 1

S/cm, which is 10 times greater than that of electrolyte. The BCFZ-5 has conductivity

of 5.5 S/cm at 600oC in air atmosphere. Therefore, it can also be used as cathode

material for solid oxide fuel cell.

It has been pointed out by Bin Zhu [1-2] that if a material has to be used as a cathode

or anode material then, its conductivity should be at least 10 times more than that of

the electrolyte. In this present work, NKCDC electrolyte shows a conductivity of 0.1

S/cm [15], whereas BCFZ-5 possesses a conductivity of 25.84 and 5.5 S/cm at

hydrogen and air atmosphere, respectively. Therefore, it is concluded that BCFZ-5 is

a promising candidate for both anode and cathode.


125

300 350 400 450 500 550 600-5

0

5

10

15

20

25

30

Ele

ctr

ica

l C

on

du

ctiv

ity (

S/c

m)

Temperature (oC)

BCFZ-1 BCFZ-2 BCFZ-3 BCFZ-4 BCFZ-5 BCFZ-6

Hdrogen Atmosphere

Figure 5.33: Electrical DC Conductivities of BCFZ (1-6) Materials at H2 Atmosphere

300 350 400 450 500 550 600-1

0

1

2

3

4

5

6

Ele

ctr

ica

l C

on

du

ctiv

ity

(S

/cm

)

Temperature (oC)

BCFZ-1 BCFZ-2 BCFZ-3 BCFZ-4 BCFZ-5 BCFZ-6

AIR Atmosphere

Figure 5.34: Electrical DC Conductivities of BCFZ (1-6) Materials at Air Atmosphere


126

Table 5.11: Particle Size, Activation Energy and Electrical Conductivity Data

Sample’s Name

Temp. Range (o C)

Particle Size (nm)

Activation Energy (Ea) (eV)

DC Conductivity (S/cm) at 600oC

At H2 At AIR At H2 At AIR

BCFZ-1 300-600 58.16 2.38X10-2 25.09X10-2 0.86 0.84

BCFZ-2 300-600 35.86 1.22X10-2 14.10X10-2 1.94 1.20

BCFZ-3 300-600 56.84 8.60X10-2 14.30X10-2 4.55 3.00

BCFZ-4 300-600 38.46 8.38X10-2 8.14X10-2 6.14 4.15

BCFZ-5 300-600 25.28 7.14X10-2 8.10X10-2 25.84 5.50

BCFZ-6 300-600 31.79 12.34X10-2 11.12X10-2 1.31 0.09


The activation energies of BCFZ (1-6) anode have been calculated by drawing

Arrhenius plots of DC conductivities at hydrogen and air atmosphere. The activation

energies were calculated from the linearly fitted curve by using a formula:

!

Where σ is electrical conductivity, T is temperature in kelvin, A is the exponentional

factor, k is Boltzman’s constant and Ea is the activation energy. The results are listed

in Table 5.11. The Arrhenius plot and linear fit curve of BCFZ-5 anode material has

been shown in Figure 5.35 and 5.36 at hydrogen, and air atmosphere, respectively.

The minimum values of activation energies of BCFZ-5 have been found to be 0.083

and 0.081eV at hydrogen and air atmosphere, respectively.


127

1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8

9.4

9.5

9.6

9.7

9.8

9.9

10.0

10.1

1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.99.3

9.4

9.5

9.6

9.7

9.8

9.9

10.0

10.1

Linear Fit

Ea = 7.14x10-2

ln σσ σσ

T (S/c

m.K

)

Temperature (K-1)

Linear Fit Data of BCFZ-5 at H2 Atmosphere

ln σσ σσ

T (

S/c

m.K

)

1000/T (K-1)

Arrhenius Plot of BCFZ-5 at H2 Atmosphere

Figure 5.35: Arrhenius Plot of BCFZ-5 from DC Conductivity at H2 atm.

1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.87.8

7.9

8.0

8.1

8.2

8.3

8.4

8.5

1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9

7.5

7.6

7.7

7.8

7.9

8.0

8.1

8.2

8.3

Linear Fit Data of BCFZ-5 at AIR Atmosphere

Linear Fit

Ea = 8.10x10

-2

ln σσ σσ

T (

S/c

m.K

)

Temperature (K-1)

ln σσ σσ

T (

S/c

m.K

)

1000/T (K-1)

Arrhenius Plot of BCFZ-5 at AIR Atmosphere

Figure 5.36: Arrhenius Plot of BCFZ-5 from DC Conductivity at Air Atmosphere


128

5.4.6 Electrochemical Impedance Spectroscopy (EIS)

The electrochemical impedance spectroscopy of pure BCFZ-5 electrode material

was observed by VERSASTAT-2273 Potentistat under hydrogen atmosphere at

different temperatures in range of 300-600oC. The frequency range was adjusted

between 0.01 Hz to 1 MHz. The results shown in Figure 5.37(a-g) indicate that the

BCFZ-5 electrode materials possess very low resistances over the temperature range

of 300-600oC with an interval of 50oC. It can be seen that the resistances decrease

with increase of temperature. From the impedance spectra, it can be observed that at

high frequency end there exists an inductive reactance due to the device and the

connecting leads. The depressed arc comes into view at medium and low frequency

yielding some information about the conduction mechanism of the electrode. This

material temperature exhibits good conductivities at hydrogen atmosphere; the values

are listed in Table 5.11.


129


130


131

Figure 5.37(a-g): AC Impedance Spectroscopy of Pure BCFZ-5 Anode Material

in Temperature Range (300-600oC)

Figure 5.38 shows the Electrochemical Impedance Spectroscopy (EIS) of

composite anode (80 wt. % BCFZ-20 wt. % NKCDC) at a fixed temperature 450oC

under hydrogen atmosphere in the frequency range of 0.01Hz to 1MHz. The


132

imaginary part of impedance was plotted against the real part of the impedance. The

experimental results exhibit two semicircles. One circle emphasizes the response of

the bulk and grain boundaries of the sintered anode material. The arc in second semi-

circle revealed the number of other resistances such as due to device and connecting

leads etc. The left side arc lies in high frequency region and the part of arc on right

side of the circle lies in low frequency region. The depressed arc revealed the

maximum anode contribution in the spectra. Hence, the experimentally measured and

simulated data can be directly compared, the equivalent circuit LRQ(CR) fitting is

used for the interpretation of EIS data. Where L, R, C and Q denotes the inductance

caused by the cables, ohmic resistance either in high frequency arc region or in low

frequency arc region, C corresponds to constant phase element and Q represents the

charge respectively.

0 5 10 15 20 25 30 35 40

0

2

4

6

8

10

Zim

(oh

m)

Zre (Ohm)

Experimental Curve Simulated Curve

Temperature 450oC

C

R

Figure 5.38: AC Electrochemical Impedance Spectroscopy of BCFZ-5 Anode,

Experimental and Simulated Curve at 450oC


133

5.4.7 Fuel Cell Performance Measurements

In order to study the fuel cell performance, fuel cells were constructed in such

a way that both the anode and the cathode consisted of the same material. For

instance, NK-CDC electrolyte was sandwiched between two BCFZ-1 electrodes; one

as anode and other as cathode. The other cells were constructed in same way by using

BCFZ-2 to BCFZ-6 material. Hydrogen (fuel) is supplied at anode side and air

(oxidant) is supplied at cathode side to perform the experiment. The resulting open

circuit voltage, current densities and power densities were measured at 550oC. The

results of measurements are shown in Figure 5.39 and listed in Table 5.12. The

maximum values of open circuit voltage (OCV) were found to be 0.950, 0.980, 1.005,

0.97, 1.007 and 0.82 V for symmetrical BCFZx-NKCDC/NKCDC/BCFZx-NKCDC

(where x = 1, 2, 3, 4, 5 and 6) fuel cell, respectively. The results indicate that the fuel

cell containing BCFZ-5-NKCDC/NKCDC/BCFZ-5NKCDC electrode system exhibits

the highest performance of 741.87mW/cm2. Unfilled emblem show the plot of current

density versus power density and filled emblems exhibit the plot of current density

versus voltagein the Figures 5.39 and 5.40.


134

0 500 1000 1500 2000 2500

0.0

0.2

0.4

0.6

0.8

1.0

1.2

-100

0

100

200

300

400

500

600

700

800

Po

wer

den

sity

(m

W/c

m2)

Op

en

Cir

cuit

Volt

age (

V)


BCFZ-1

BCFZ-2

BCFZ-3

BCFZ-4

BCFZ-5

BCFZ-6

T = 550oC

Figure 5.39: Symmetrical Fuel Cell Performances of BCFZx at 550oC using NKCDC Electrolyte, Where x = 1, 2, 3, 4, 5 and 6

The BCFZ-5 anode has also been tested with BSCF cathode material in order

to see if it could yield better performance. The measurements were conducted in the

temperature range of 400-550oC. The results of measurements are shown in Figure

5.40 and are illustrated in Table 5.13. The maximum power densities were found to be

933mW/cm2, 717mW/cm2, 715mW/cm2 and 636mW/cm2 at the temperatures of 550,

500, 450 and 400oC respectively, when hydrogen was supplied as fuel at anode side at

the rate of 100ml/min and air as oxidant at cathode side. The values of OCVs were

observed to be 1.07, 1.02, 1.02 and 1.0 V at the same temperatures.


135

0 500 1000 1500 2000 25000.0

0.2

0.4

0.6

0.8

1.0

1.2

0

200

400

600

800

1000

Pow

er D

ensi

ty (

mW

/cm

2)

Volt

age

(V)


T550oC

T500oC T450oC

T400oC

Figure 5.40: Performance of BCFZ-5-NKCDC/NKCDC/BSCF-NKCDC Fuel Cell in Temperature Range of 400-550oC

Table 5.12: Performance of Symmetrical BCFZ (1-6) Fuel Cell

Cell Category

Temp. ( o C) Max. OCV (V)

Max. Current Density (mA/cm2)

Max. Power Density (mW/cm2)

BCFZ-1 550 0.95 172 40.30

BCFZ-2 550 0.98 1517.03 468.11

BCFZ-3 550 1.005 2043.24 633.90

BCFZ-4 550 0.97 1857 545.82

BCFZ-5 550 1.007 2260.79 741.87

BCFZ-6 550 0.82 810.5 171.59

5.4.8 Stability Measurement

The stability of the cell having BCFZ-5 anode was recorded continuously for

24 hours with a regular interval of half an hour. The cell OCV measured at

temperature 550oC exhibited almost stable performance. The measurements of


136

performance are shown in Figure 5.41(a). The average power density of 800mW/cm2

was observed during this period and is shown in Figure 5.41(b).

0 2 4 6 8 10 12 14 16 18 20 22 240.0

0.2

0.4

0.6

0.8

1.0

1.2

OC

V (

V)

T ime (h)

→

(a)

A verage open c ircu it voltage abou t 1 V of

so lid ox ide fue l cell based on

B C FZ electrode/anode opera ted w ith

hydrogen(fue l) and a ir (ox idan t)

a t a tem peratu re o f 550oC

Figure 5.41(a):Short-term Stability for open circuit voltage test of cell at 550oC

0 3 6 9 12 15 18 21 24500

550

600

650

700

750

800

850

900

950

1000

Po

wer

Den

sity

( m

W/c

m2 )

T im e (h )

A vera g e P o w er D ens ity = 8 0 0m W /cm2

T em p eratu re = 5 50oC

(b)

Figure 5.41(b): Short-term Stability for power density test of cell at 550oC

Table 5.13 : Performance of Non-Symmetrical BCFZ-5 Fuel Cell

Cell Category

Fuel Cell Components Fuel Cell Performance at 550oC

Composite

Anode

Composite

Electrolyte

Composite

Cathode

Max.

OCV (V)

Max. C.D.

(mA/cm2)

Max. P.D.

(mW/cm2)

BCFZ-5 BCFZ-5-

NKCDC

NKCDC BSCF-

NKCDC

1.07 2328.12 933.41


137

5.4.9 Cost Analysis

The cost analysis has been done for BCFZ-5 electrode/anode and it has been

found that BCFZ-5 electrode/anode has exhibited reliable open circuit voltage, power

density with hydrogen (fuel) and air (oxidant) at comparatively low temperature of

550oC. This is the unique electrode, which has specified a competitive alternative

candidate to replace the conventional electrode Ni-YSZ in solid oxide fuel cell.

Rather than its cost has been found the most cheap in all aspects including raw

materials, shipment, power cost, laboratory cost, researcher’s salaries and others. The

present estimated ground cost has been calculated 30€/20 grams for fine powder and

its cost can be further reduced by large scale manufacturing. However, the cost of

conventional Ni-YSZ electrode is reported on Sigma Aldrich website is 57.74€/20

gram powder. The present cost of BCFZ-5 electrode/anode powder elucidate that the

BCFZ-5 electrode/anode is almost 50% cheap than that of conventional Ni-YSZ

electrode on small scale manufacturing. The evaluated cost of this electrode has been

illustrated in Table 5.14;

Table 5.14: Estimated Cost of BCFZ-5 Electrode (Ba0.05Cu00.25Fe0.10Zn0.60)


BaCO3 2.80 6.891 893.106

CuCO3Cu(OH)2 15.70 2.763 358.108

Fe(NO3)3.9H2O 12.50 33.40 4329

Zn(NO3)2.6H2O 69.00 6.058 785.194

BCFZ Total Cost / 100g 49.112 6365

Sintering Present Charges 10 Commercial Units 2.00 260

Labor Cost Researcher per day Salary 8 1050


Total Cost After sintering G. T / 40 gram 60 7776


138

5.4.10 CONCLUSIONS

The Ba0.05Cu0.25Fe0.10Zn0.60 possesses hexagonal structure as indexed by XRD.

The sintering temperature 800oC for 4 hours produces well crsytallinity.

BCFZ exhibits the conductivity values of 25.84 and 5.5 S cm−1 at hydrogen

and air atmosphere respectively.

The values of activation energy were found to be 0.0831 and 0.081eV

The presence of depressed semi-circle in electrochemical impedance spectra

shows that the maximum contribution comes from BCFZ anode.

The BCFZ anode based on doped ceria electrolytes employed a new concept

of Ni free fuel cell and proved to be a valid alternative to the traditional SOFC

configurations with the power density of 933mW/cm2 at 550oC.

It is the optimized new Zn based electrode usually used as anode with

NKCDC electrolyte and BSCF [17-19] cathode having almost same voltage,

current density and power density as conventional fuel cell of Ni-cermet with

YSZ electrolyte. This new Zn based electrode extensively approaches to achieve

a target for fuel cell community. The previous and next electrodes discussed in

this dissertation basically support to search out an alternative electrode by

adjusting the amount of Zn in molar percentage including different catalysts.

These catalysts of course enhance the electrochemical properties of the material.

Iron is an extensive catalyst, whose 1 % molar ratio performs an equivalent

performance to conventional fuel cell.

We have succeeded in preparing new low cost electrodes for fuel cell which

requires low manufacturing cost and operating temperature.

A detailed material cost comparison has shown at the end of this thesis in

Annexure-4.


139

5.5 Sample No.5 ---------- Ba0.15Fe0.10Ti0.15Zn0.60 (BFTZ)

5.5.1 Introduction

This sample consists of Ba0.15 Fe0.10Ti0.15Zn0.60 (BFTZ) anode material. For

conductivity measurement, the pure BFTZ anode was tested while for performance

test, 20 wt. % NKCDC and NSDC electrolytes were added with BFTZ to make it

composite anode of BFTZ-NKCDC and BFTZ-NSDC in a ratio of 80 wt. % BFTZ

and 20 wt. % NKCDC/NSDC. Fuel cell based on BFTZ anode material was tested by

using NKCDC electrolyte and BSCF cathode material. This anode material was also

tested using NSDC conventional electrolyte. The characterization and electrochemical

properties have been studied in detail and are discussed below:

5.5.2 Crystallographic Analysis

The XRD patterns were recorded for the composition of Ba0.15Fe0.10Ti0.15Zn0.60

anode material by Philips X'Pert X-Ray Diffractometer fitted with an X'Celerator

detector using Ni filtered Cu-Kα radiation (λ=1.54056 Å) in flat plate θ/θ geometry.

The X-ray data were collected in the range of 10–80°, with a scan time of 100 s per

step, in steps of 0.02° at room temperature. The results are shown in Figure 5.42 and

are listed in Table 5.15. The XRD patterns indicate that structure is single phase with

dominating ZnO compound and the Ti peaks seems to be shifted into Zn during the

sintering process, because no peak of Ti was observed in XRD pattern. However, few

peaks of BaFeO were found by analyzing with Jade-5 software at 2θ angles of 31.48,

38.77 and 45.15. Indexation of all the peaks reveals that the structure exhibits

hexagonal structures. The average crystalline size of BFTZ was calculated by

applying Scherer’s formula and found to be 39.17 nm.


140

Figure 5.42: Crystallographic View of Ba0.15Fe0.10Ti0.15Zn0.60(BFTZ) Anode Material

5.5.3 Electrical Conductivity Measurements

The electrical DC and AC conductivities of BFTZ were measured in the

temperature range of 300-600oC at hydrogen atmosphere by Digital Micro-ohm

Meter, KD-2531, China and VERASTAT 2273 Potentiometer, respectively. The

results of measurements are shown in Figure 5.43 and are listed in Table 5.15. The

results depicted that both the conductivities increase with increasing temperature. The

BFTZ possesses the highest DC and AC conductivity value of 5.86 and 4.81 S/cm,

respectively at 600oC in hydrogen atmosphere. The AC conductivities were found

slightly less than measured DC conductivity over the same temperature range. Both

the conductivities increase linearly at intermediate temperature. This linearly

increasing trend of conductivities corresponds to better performance at intermediate

temperatures.

0

500

1000

1500

2000

2500

Inte

nsity(C

ou

nts

)

36-1451> Zincite - ZnO

14-0180> BaFeO3 - Barium Iron Oxide

20 30 40 50 60 70

2-Theta(°)

[45.ASC] 10.008 193


141

300 350 400 450 500 550 6002.5

3.0

3.5

4.0

4.5

5.0

5.5

6.0

6.5

Con

du

cti

vit

y (

S/c

m)

Temperaure (oC)

DC Condctivity AC Conductivity

Hydrogen Atmosphere

Figure 5.43: Electrical DC and AC conductivity of BFTZ at Hydrogen Atmosphere

Table 5.15: Particle Size, Conductivity and Activation Energy of BFTZ Anode

Sample Category Particle Size (nm)


Conductivity in H2 at 600oC (S/cm)

DC AC DC AC

BFTZ 39.17 0.15 0.14 5.86 4.81


In order to calculate the activation energy of BFTZ anode material, Arrhenius

plots were drawn from the DC and AC conductivity data in hydrogen atmosphere.

Linear fitting technique was applied to find out the activation energy from the

conductivities data by using Arrhenius equation;

!

Where σ is conductivity, A is pre-exponential factor, k is Boltzmann’s constant, T is

absolute temperature in kelvin and Ea is the Activation Energy in eV. The results of


142

measurements are shown in Figure 5.44 and 5.45, and are listed in Table 5.15. The

linear fit data has also been shown in the inset in Figure 5.44 and 5.45.

The activation energy was found to be 0.15 and 0.14eV from DC and AC conductivity

data, respectively at hydrogen atmosphere. This small value of activation energy

emphasizes that the fuel cell can take a short time to start the chemical reaction.

1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8

7.6

8.0

8.4

8.8

9.2

9.6

1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.97.2

7.4

7.6

7.8

8.0

8.2

8.4

8.6

8.8

ln σσ σσ

T (S

/cm

.K)

1000/T (K-1)

Ea = 0.15 eVLinear Fit

Linear Fit Data of BFTZ at H2 Atmosphereln

σσ σσT

(S

/cm

.K)

1000/T (K-1)

Arrhenius Plot from DC Conductivity Data

H 2 A

tmos

pher

e

Figure 5.44: Arrhenius Plot of BFTZ from DC Conductivity Data at H2 Atmosphere

1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.87.2

7.4

7.6

7.8

8.0

8.2

8.4

8.6

1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.97.0

7.2

7.4

7.6

7.8

8.0

8.2

8.4

8.6

Linear Fit Data of BFTZ at H2 Atmosphere

Linear Fit

Ea = 0.14 eV

ln σσ σσ

T (

S/c

m.K

)

1000/T (K-1)

H 2 A

tmos

pher

e

Arrhenius Plot from AC Conductivity Data

ln σσ σσ

T (

S/c

m.K

)

1000/T (k-1)

Figure 5.45: Arrhenius Plot of BFTZ from AC Conductivity Data at H2 Atmosphere


143


In order to measure the performance of fuel cell based on BFTZ anode material, two

different types of fuel cells were fabricated having NKCDC or conventional NSDC

electrolyte and BSCF conventional cathode. For this purpose, the composed fuel cells are

categorized as:

(a) BFTZ-NKCDC/NKCDC/BSCF

(b) BFTZ-NSDC/NSDC/BSCF

The performance of this anode material was measured in the temperature range of

400-500oC. The values of open circuit voltage, current densities were measured

experimentally using fuel cell testing unit L-43, China. Hydrogen was provided (fuel)

at anode side at a rate of 100ml/min and air (oxidant) at cathode side during this

experiment. The results of measurements are shown in Figure 5.46(a) and 5.46(b), and

are listed in Table 5.16. It has been found that this anode material can provide better

performance results with conventional electrolyte NSDC instead of NKCDC

electrolyte while both electrolyte materials have the same structural and

electrochemical properties. It can therefore be inferred from these results that the

BFTZ anode material is more compatible with NSDC conventional electrolyte instead

of other electrolytes like NKCDC. The maximum values of open circuit voltage and

power density were found to be 0.95 V and 470.62mW/cm2, respectively.


144

-100 0 100 200 300 400 500 6000.0

0.2

0.4

0.6

0.8

1.0

-30

0

30

60

90

120

150

Po

wer

Den

sity

(m

W/c

m2)

Volt

age

(V)


550OC

500OC

450OC

400OC

Figure 5.46(a): Performance of Fuel Cell having BFTZ Anode, NKCDC Electrolyte

and BSCF Cathode

0 200 400 600 800 1000 1200 1400 16000.0

0.2

0.4

0.6

0.8

1.0

1.2

0

100

200

300

400

500

Pow

er D

en

sity

(m

W/c

m2)

Volt

age (

V)


T550oC

T500oC

T450oC

T400oC

Figure 5.46(b): Performance of Fuel Cell having BFTZ Anode, Conventional NSDC

Electrolyte and BSCF Cathode


145

Table 5.16: Performance Data of BFTZ Anode Material

Cell Category

Fuel Cell Construction Fuel Cell Performance at 550oC

Anode Electrolyte Cathode Max. OCV (V)

Max.*C.D. (mA/cm2)

Max. *P. D. (mW/cm2)

(a) BFTZ-

NKCDC

NKCDC BSCF 0.910 585.94 126.81

(b) BTFZ-

NSDC

NSDC BSCF 0.950 1550 470.62

*C. D. stands for current density and *P. D. stands for power density

5.5.6 Cost Analysis

The cost of BFTZ anode material has been calculated based on raw materials,

power consumption, labor and others and has been depicted in Table 5.17. In this

electrode, Cu has been replaced by Ti, and TiO2 is very cheap as compared to Cu

compound. This new alternative anode material for solid oxide fuel cell can be made

fruitful results in cost reduction. However the further work to enhance the power

density of solid oxide fuel cell based on BFTZ material will be extended in future.

Table 5.17: Estimated Cost of BFTZ Electrode (Ba0.15Fe0.10Ti0.15Zn0.60)


BaCO3 11.35 27.24 3530.44

Fe(NO3)3.9H2O 15.50 2.72 353.54

TiO2 4.60 0.25 33.38

Zn(NO3)2.6H2O 68.55 6.05 780.20

BFTZ Total Cost / 100g 36.28 4700.00






146

5.5.7 CONCLUSIONS

Ba0.15Fe0.10Ti0.15Zn0.60 composition synthesized by solid state reaction method

possesses hexagonal structure as analyzed by Jade-5 Software.

The particle size of BFTZ was found to be 39.17 nm.

The maximum value of OCV and power density was found to be 0.95 V and

470.625mW/cm2 at temperature 550oC, respectively.

Its present cost has been calculated 25€/20 gram, however the enhancement

of power density is in under concern

This material is an introduction of addition of TiO2 in fabrication of

electrodes materials. It has also been noticed that the compound TiO2 is

cheaper than that of others compound. The further work on this material will

be extended in future research work.


147

5.6 Sample No. 6 ---------- Sodium-Potassium Carbonated

Calcium Doped Ceria (NK-CDC) Electrolyte

This sample consists of Sodium-Potassium Carbonated, Calcium Doped Ceria

(NK-CDC) electrolyte material. The NK-CDC electrolyte material was prepared by

co-precipitation method. This material is the central part of the fuel cell, the

performance of the fuel cell depends on the compatibility of electrolyte and electrode.

The proposed electrolyte material was found compatible to the BCFZ and other

electrodes. In this electrolyte, a very cheap material Ca(NO3).4H2O was doped with

ceria instead of precious materials like Gd(NO3)3.6H2O and Sm(NO3)3.6H2O. The

detail of this part of the thesis work has been published in “Journal ofFuel Cell

Science and Technology” Volume, 8, Issue 4, (2011); Pages: 041013 and the copy of

the paper is attached as an Annexure-2 on page XXIV.


148

5.7 Sample No. 7 ---------- Yttrium Oxide Coated Gadolinium

Doped Ceria (GDC-Y2O3) Electrolyte

This sample consists of Ytttria Oxide coated on Gadolinium Doped Ceria (Y-

GDC) electrolyte material. Oxide based two phase composite electrolyte

(Ce0.9Gd0.1O2–Y2O3)was synthesized by co-precipitation method. The nanocomposite

electrolyte showed the significant performance of power density 785mW/cm2 and

higher conductivities at relatively low temperature 550°C. Ionic conductivities were

measured with ac impedance spectroscopy and four-probe dc method. The structural

and morphological properties of the prepared electrolyte were investigated by

scanning electron microscope (SEM). The thermal stability was determined with

differential scanning calorimetry. The particle size that was calculated with Scherer’s

formula, 15–20 nm, is in a good agreement with the SEM and X- ray diffraction

results. The purpose of this study is to introduce the functional nanocomposite

materials for advanced fuel cell technology to meet the challenges of solid oxide fuel

cell. The detail of this part of the thesis work has been published in “Journal of Fuel

Cell Science and Technology” Volume, 8, Issue 4, (2011); Pages: 041012 and the

copy of the paper is attached as an Annexure-3 on page XXV.


149

5.8 Sample No. 10 ---------- Ba0.4Sr0.6Co0.3Mn0.7O3-δ (BSCM)

5.8.1 Introduction

This cathode material was prepared by wet chemical method as described

earlier in section 4.3.3.1 and Figure 4.1. In order to measure its conductivity of the

material, a pellet of diameter 13 mm and 3 mm thickness was made by using

hydraulic press. While for performance test, 20 wt. % NKCDC and conventional

NSDC electrolytes were added separately with BSCM to make it composite cathode.

Two composite cathodes were prepared with BSCM. For this purpose, it was mixed

with two electrolytes separately in following distribution:

1. 80 wt. % of BSCM and 20 wt. % NKCDC

2. 80 wt. % of BSCM and 20 wt. % NSDC

Composite BCFZ-5 and conventional Ni based anodes were used as an ode to make

complete fuel cell. The BSCM material was characterized by XRD, SEM and

electrochemical techniques.

5.8.2 X-Ray Diffraction Pattern

Figure 5.47 shows the XRD pattern of the BSCM material sintered at 800oC

for four hours. The results emphasize that the material has two phases, while SrO has

been fully doped into the BaCoMn. It has also been seen from the XRD pattern that

the material has very strong peaks at small angles, while the peaks were found

comparatively week at large angle > 44o. This could be the result of some impurities

in the material. The particle size was calculated from the XRD data by Scherer’s

formula and found to be 49.09 nm from the peak at 2θ angle of 31.51o.


150

Figure 5.47: XRD Pattern of Ba0.4Sr0.6Co0.3Mn0.7O3-δ(BSCM) Cathode

5.8.3 Scanning Electron Microscopic (SEM) View

Figure 5.48 exhibits the microstructure of the material, which shows that the

BSCM cathode material is porous and have nanostructure in the range of 20-50nm. It

has been reported that smaller particle size enhances the conductivity of the cell as it

allows more and more ions to pass through the interface [20].

Figure 5.48: Microstructure of BSCM Cathode Material by SEM Analysis

0

100

200

300

400

500

600

Inte

nsity(C

ou

nts

)

52-1612> BaCoO3 - Barium Cobalt Oxide

26-0169> BaMnO3-x - Barium Manganese Oxide

20 30 40 50 60 70

2-Theta(°)

[16.ASC] 10.008 229


151

5.8.4 DC Conductivity Measurements

The electrical conductivities of BSCM cathode material were measured by

KD-2531 Digital Micro-ohm Meter, China in a temperature range of 300-600oC at air

and hydrogen atmosphere. The results of measurements are shown in Figure 5.49 and

listed in Table 5.18. The results show that the DC conductivity at air atmosphere

increases gradually but not linearly with increasing temperature. On the other hand,

the DC conductivity at hydrogen atmosphere decreases linearly with increasing

temperature. The DC conductivity values were found to be 37 and 17 S/cm at air and

hydrogen atmosphere, respectively at 600oC. This value is about 40 times grater than

that of the electrolyte (NK-CDC and conventional NSDC) used in the present work.

Both the electrolytes have a conductivity of 0.1 S/cm at 600oC [21]. It has been

observed that the conductivity measured at air atmosphere is 2 times more than that

measured at hydrogen atmosphere. For this reason, it would be preferable to use

BSCM as cathode in a solid oxide fuel cell.

300 350 400 450 500 550 6005

10

15

20

25

30

35

40

Co

nd

uct

ivit

y (

S/c

m)

Temperature (oC)

DC Conductivity at AIR Atmosphere DC Conductivity at H

2 Atmosphere

Figure 5.49: DC Conductivity of Pure BSCM Cathode at Air and H2 Atmosphere


152

5.8.5 AC Conductivity Measurements

The AC conductivities has also been measured at air and hydrogen atmosphere

in the temperature range of 300-600oC by using VERSASTASTAT-2273. The results

are shown in Figure 5.50 and listed in Table 5.18. The conductivity of the material

increases with increasing temperature at both air and hydrogen atmosphere. The

measurements data possesses almost equal conductivity value over a temperature

range of 300-550oC, however, the difference between both the conductivities was

found at 600oC. The AC conductivities were found to be less than DC conductivities

due to the inductive reactance of wires, leads and sample holder.

300 350 400 450 500 550 6000

1

2

3

4

5

6

7

8

Co

nd

ucti

vit

y (

S/c

m)

Temperature (oC)

AC Conductivity at AIR Atmosphere AC Conductivity at H

2 Atmosphere

Figure 5.50: AC Conductivity of Pure BSCM Cathode at Air and H2Atmosphere Table 5.18:Particle Size, ASR, Activation Energy and Conductivity of BSCM Cathode

Sample Category

Particle Size (nm)

ASR (Ωcm2)

Activation Energy from DC

Conductivity (eV)

DC Conductivity at 600oC (S/cm)

AC Conductivity at 600oC (S/cm)

AIR H2 AIR H2 AIR H2

BSCM

49.09

0.07

0.49

0.46

37

17

6.94

4.18


153

5.8.6 Area Specific Resistance (ASR)

Figure 5.51 shows the area specific resistance ASR of BSCM cathode material

measured as a function of temperature at hydrogen atmosphere. A minimum value of

area specific resistance was found to be 0.07Ω.cm2 at 550 and 600oC. It varied from

0.07 to 0.28Ω.cm2 during fall in temperature from 600 to 300oC. This ASR is lower

than that of LSCF and SSC cathode as discussed in section 2.3.3.

250 300 350 400 450 500 550 600 6500.05

0.10

0.15

0.20

0.25

0.30

Are

a S

pec

ific

Res

ista

nce

(ΩΩ ΩΩ

.cm

2)

Temperature (oC)

Area Specific Resistance (ASR)

Figure 5.51: Area Specific Resistance of BSCM at Hydrogen Atmosphere


The Arrhenius plots were drawn from the DC conductivities measured at air

and hydrogen atmosphere and activation energy was calculated using linear fitting

technique with an Arrhenius equation;

!

Where σ is the conductivity, A is pre-exponential factor, k is Boltzmann’s constant, T

is absolute temperature in kelvin and Ea is the Activation Energy. The Arrhenius


154

curve has been shown in figure 5.52 and 5.53 at air and hydrogen atmosphere,

respectively with linear fit data in the inset. The results of measurements are listed in

Table 5.18. The activation energy was found to be 0.26 and 0.46 eV at air and

hydrogen atmosphere, respectively. This shows, this cathode material takes very short

time to start the chemical reaction in the fuel cell.

1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.88.0

8.5

9.0

9.5

10.0

10.5

Arrhenius Plot at Air Atmosphere

1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9

8.0

8.5

9.0

9.5

10.0

10.5

ln σσ σσ

T (

S/c

m.K

) Linear Fir Data

1000/T (K-1)

Ea = 0.26 eV

Linear Fit

ln σσ σσ

T (

S/c

m.K

)

1000/T (K-1)

Ea = 0.26 eV

Figure 5.52: Arrhenius Plot of BSCM Cathode at AirAtmosphere

1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.86.0

6.5

7.0

7.5

8.0

8.5

Arhenius Curve at Hydrogen Atmosphere

1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9

6.0

6.5

7.0

7.5

8.0

8.5

ln σσ σσ

T (

S/c

m.K

)

Temperature (K-1)

Ea = 0.46 eV

Linear Fit

ln σσ σσ

T (

S/c

m.K

)

1000/T (K-1)

Ea = 0.46 eV

Figure 5.53: Arrhenius Plot of BSCM Cathode at Hydrogen Atmosphere


155


The AC Electrochemical Impedance Spectroscopy was carried out in a

frequency range of 0.01 Hz to 1 MHz over temperature range of 300-600oC. The

experimental data and results are shown in Figure 5.54. It can be seen from the Figure

5.54 that the resistance of the material gradually increases with decrease of

temperature. It possesses the highest value at 300oC. The impedance spectra in the

Figure 5.54 give information about the distribution of resistance over the frequency

range. The semicircles in the figure show the impedance at higher frequency range

and the linear line exhibit the impedance at lower frequency. However, at lower

frequencies, resistances are high due to the contribution of wires, leads and sample

holder etc.

-10 0 10 20 30 40 50 60 70 80

2

4

6

8

10

12

14

Zim

(Oh

m)

Zre

(Ohm)

550 500 450 400 350 300

Figure 5.54: AC Electrochemical Impedance Spectra of Pure BSCM Cathode

Material


156


In order to study the performance of BSCM cathode material, four different

types of fuel cells were constructed. The results of measurements are shown in Figure

5.55(a-d) and listed in Table 5.19. Its performance has been tested by using hydrogen

as a fuel at anode side and air as an oxidant at cathode side. The values of open circuit

voltage, current densities were measured in the temperature range of 400-550oC by

the experiment using fuel cell testing unit L-43, China. The fuel cells were fabricated

in consecutive three layers of Composite Anode/Electrolyte/Composite Cathode.

For performance test, each cell was categorized as follows:

a) BCFZ-NKCDC/NKCDC/BSCM-NKCDC

b) BCFZ-NSDC/NSDC/BSCM-NSDC

c) Ni-NKCDC/NKCDC/BSCM-NKCDC

d) Ni-NSDC/NSDC/BSCM-NSDC

0 200 400 600 800 1000 1200 1400 16000.0

0.2

0.4

0.6

0.8

1.0

1.2

0

100

200

300

400

500

600

Pow

er D

en

sity

(m

W/c

m2)


Volt

age (

V)

T550oC

T500oC

T450oC

T400oC

(a)

Figure 5.55(a): Performance of Fuel Cell using BCFZ-5-NKCDC Anode,

NKCDC Electrolyte and BSCM-NKCDC Cathode


157

0 400 800 1200 1600 20000.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

0

100

200

300

400

500

600

Po

wer

Den

sity

(m

W/c

m2)

Vo

lta

ge (

V)


T550oC

T500oC

T450oC

T400oC

(b)

Figure 5.55(b): Performance of Fuel Cell using BCFZ-5-NSDC Anode, NSDC

Electrolyte and BSCM-NSDC Cathode

0 500 1000 1500 2000 25000.0

0.2

0.4

0.6

0.8

1.0

1.2

-100

0

100

200

300

400

500

600

700

800

Pow

er D

ensi

ty (

mW

/cm

2)

Volt

age

(V)


T550oC

T500oC

T450oC

T400oC

(c)

Figure 5.55(c): Performance of Fuel Cell using Ni-NKCDC Anode, NKCDC

Electrolyte and BSCM-NKCDC Cathode


158

0 400 800 1200 1600 20000.0

0.2

0.4

0.6

0.8

1.0

1.2

-100

0

100

200

300

400

500

600

700

800

Pow

er D

ensi

ty (

mW

/cm

2)

Volt

age (

V)


T550oC

T500oC T450oC

T400oC

(d)

Figure 5.55(d): Performance of Fuel Cell using Ni-NSDC Anode, NSDC

Electrolyte and BSCM-NSDC Cathode

Table 5.19 Fuel Cell Performance Data Based on BSCM Cathode Material

Cell

Category


anode electrolyte cathode OCV

(V)

Current Density

(mA/cm2)

Power Density

(mW /cm2)

BSCM (a) BCFZ NKCDC BSCM 1.01 1504.68 525.24

BSCM (b) BCFZ NSDC BSCM 1.15 1448.44 549.29

BSCM (c) Ni- NKCDC BSCM 1.02 2239.06 725.98

BSCM (d) Ni NSDC BSCM 1.002 1800 743.378

5.8.10 Cost Analysis

Data has been collected to calculate the estimate ground cost of the BSCM

material used as cathode in this research work. The details have been shown in table

5.20:


159

Table 5.20: Estimated Cost of BSCM Cathode (Ba0.4 Sr0.6Co0.3Mn0.7)


BaCO3 21.20 52.173 6652.918

Sr(NO3)2 34.00 417.52 53240.47 Co(NO3)2.6H2O 23.35 39.975 5097.477 MnCO3 21.45 2.985 315.86 BFTZ Total Cost / 100g 512.653 65430 Sintering Present Charges 10 Commercial Units 2.00 260 Labor Cost Researcher per day Salary 8 1050 Others Any extra 2.315 115.119 Total Cost After sintering G. T / 60 gram 515 65730

5.8.11 CONCLUSIONS

Ba0.4Sr0.6Co0.2Mn0.8 composition synthesized by wet chemical method

possesses hexagonal pervoskite structure.

The sintering at 800oC for 4 hours produces well crsytallinity.

BSCM cathode material has electronic conductivity of 37 S/cm in air

atmosphere at 600oC and 20 S/cm in hydrogen atmosphere at 300oC.

The conductivity at air atmosphere is higher than that with respect to

hydrogen atmosphere. This feature makes it a good choice as cathode

material.

Such low values of activation energy (0.26 and 0.46 eV) exhibit the fast

chemical reaction in the cell.

The presence of depressed semi-circle in Electrochemical Impedance Spectra

shows the maximum contribution of the BSCM cathode.

The maximum value of OCV and power density was found to be 1.02V and

743.38mW/cm2 at 550oC respectively.

The cathode material has area specific resistance of 0.07-0.28Ω.cm2 in the

temperature range of 600-300oC. This low ASR value exhibits that it could be

a good cathode.


160

5.9 Sample No. 11 ---------- La0.6Sr0.4Co0.3Zn0.7O3-δ (LSCZ)

5.9.1 Introduction

The LSCZ cathode material was prepared by wet chemical method as

described earlier in section 4.3.3.2 and shown Figure 4.2. The DC conductivities of

the material were measured by Digital Micro-ohm Meter KD-2531, China in the

temperature range of 300-600oC. For this purpose, a pellet of 13 mm diameter and

3mm thicknesses was made by hydraulic press. In order to measure the performance

of this material, the LSCZ cathode material was converted into a composite cathode

by adding 20 wt. % electrolyte (NKCDC or conventional NSDC) to obtain two

composite cathodes:

1. 80 wt. % of LSCZ and 20 wt. % NKCDC

2. 80 wt. % of LSCZ and 20 wt. % NSDC

Four different types of cells were prepared to measure the performance of

LSCZ cathode material in the temperature range of 400-550oC. The crystal structure,

particle size and morphology of the material were investigated by XRD and SEM

analysis technique. The electrochemical properties of the material were also studied

by measuring its conductivities and performance.

5.9.2 Crystallographic View

The X-Ray diffraction patterns were determined by using Philips X'Pert X-

Ray Diffractometer fitted with an X'Celerator detector using Ni filtered Cu-Kα

radiation (λ=1.54056 Å) in flat plate θ/θ geometry. The X-ray data were collected in

the range of 10–80°, with a scan time of 100 s per step, in steps of 0.02° at room

temperature. Figure 5.56 shows the XRD pattern of the LSCZ material sintered at

800oC for four hours. All the peaks were indexed and single phase hexagonal


161

pervoskite structure has been found. The XRD pattern was analyzed by Jade-5

software and it can be seen that the structure contains only ZnO peaks. The peaks of

other materials like LaO, SrO and CoO were shifted into ZnO during the sintering

process. The particle size was calculated by using Scherer’ equation and found to be

47.55 nm from the peak at 2θ angle of 36.20o.

Figure 5.56: XRD Pattern of La0.1Sr0.9Co0.2Zn0.8O3-δ (LSCZ) Cathode Material

5.9.3 Scanning Electron Microscopic (SEM) View

The microstructure of the LSCZ cathode material is shown in Figure 5.57. It

exhibits that the LSCZ cathode material is porous and have nanostructure in the range

of 20-60nm. It has been reported that smaller particle size enhances the conductivity

of the cell as it allows more and more ions to pass through the interface.

0

1000

2000

3000

4000

5000

6000

Inte

nsity(C

ou

nts

)

36-1451> Zincite - ZnO

20 30 40 50 60 70

2-Theta(°)

[17.ASC] 10.008 307


162

Figure 5.57: Microstructure of LSCZ Material by SEM Analysis

5.9.4 Electrical DC Conductivity Measurements

The electrical DC conductivity of LSCZ cathode material was measured at air

and hydrogen atmosphere by using Digital Micro-ohm Meter KD-2531, China in a

temperature range of 300-600oC. The results of measurements are shown in Figure

5.58 and listed in Table 5.21. The results show that the DC conductivity at air

atmosphere and hydrogen atmosphere increases gradually and linearly with increasing

temperature. The values of DC conductivity were found to be 20.29 and 4.88 S/cm at

600oC under air and hydrogen atmosphere, respectively. It can be seen that the

measured value of conductivity at air atmosphere is about 20 times grater than that of

the electrolytes NK-CDC and conventional NSDC used in the present work. Both the

electrolytes have a conductivity of 0.1 S/cm at 600oC. It has been observed that the

conductivity of LSCZ material at air atmosphere is 5 times greater than that measured


163

under hydrogen atmosphere. From the conductivity results, it is expected that LSCZ

cathode material can improve the performance of a solid oxide fuel cell.

300 350 400 450 500 550 6000

5

10

15

20

25

Hydrogen Atmosphere AIR Atmosphere

Co

nd

uct

ivit

y (

S/c

m)

Temperature (oC)

DC Conductivity of LSCZ Cathode Material

Figure 5.58: DC Conductivity of LSCZ Cathode Material at Air and H2 Atmosphere

5.9.5 Electrical AC Conductivity Measurements

The AC conductivity has also been measured at air and hydrogen atmosphere

in the temperature range of 300-600oC by using VERSASTASTAT-2273,

Potentiostat. The results are shown in figure 5.59 and listed in Table 5.21. The

conductivity of the material increases with increasing the temperature at both air and

hydrogen atmosphere. The AC conductivities were found to be 9.92 and 6.69 S/cm at

600oC under air and hydrogen atmosphere, respectively. However, the measured AC

conductivity values are less than that of DC conductivity values.


164

300 350 400 450 500 550 600

2

3

4

5

6

7

8

9

10

Con

du

cti

vit

y (

S/c

m)

Temperature (oC)

AIR Atmosphere Hydrogen Atmosphere

AC Conductivity of LSCZ

Figure 5.59: AC Conductivity of LSCZ Cathode Material at Air and H2 Atmosphere

Table 5.21: Particle Size, ASR, Activation Energy and Conductivity of LSCZ

Sample Category

Particle Size (nm)

ASR (Ωcm2)

Activation Energy from DC

Conductivity (eV)

Conductivity (S/cm) at 600oC

DC AC

AIR H2 AIR H2 AIR H2

LSCZ

47.55

0.03

9.1x10-2

9.9x10-2

20.29

4.78

9.92

6.69

5.9.6 Area Specific Resistance (ASR)

The area specific resistance of the material was measured as a function of

temperature at hydrogen atmosphere in temperature range of 300-600oC having an

active area of 0.64 cm2 of the cell. The results of measurements are shown in Figure

5.60 and listed in Table 5.21. A minimum value of area specific resistance was found

to be 0.03Ω.cm2 at 600oC. It varied from 0.03 to 0.63Ω.cm2 during fall in temperature

from 600 to 300oC. This ASR is quite lower than that of BSCM at the same

temperature range as discussed in section 5.8.6.


165

300 350 400 450 500 550 6000.02

0.03

0.04

0.05

0.06

0.07

Area Specific Resistance (ASR)

Area S

peci

fic R

esi

stan

ce (

ΩΩ ΩΩ.c

m2)

Temperature (oC)

Figure 5.60: Area Specific Resistance (ASR) of LSCZ Cathode Material


In order to calculate the activation energy of the material, the Arrhenius plots

were drawn from DC conductivity data at air and hydrogen atmosphere. The

activation energy was calculated by using linear fitting technique with Arrhenius

equation;

!

Where σ is conductivity, A is pre-exponential factor, k is Boltzmann’s constant, T is

absolute temperature in kelvin and Ea is the Activation Energy. The results of

measurement are shown in Figure 5.61 and 5.62, and the linear fit curve was shown in

inset of Figure 5.61 and 5.62 at air and hydrogen atmosphere, respectively. The values

of activation energy were found to be 9.1 X 10-2 and 9.9 X 10-2 eV at air and

hydrogen atmosphere, respectively.


166

1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.89.1

9.2

9.3

9.4

9.5

9.6

9.7

9.8

9.9

Arrhenius Plot at AIR Atmosphere

1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9

9.0

9.1

9.2

9.3

9.4

9.5

9.6

9.7

9.8

9.9

0 2 4 6 8 10

ln σσ σσ

T (

S/c

m.K

)

1000/T (K-1)

Linear Fit Data

Ea = 9.1 X

10 -2

Linear Fitln

σσ σσT

(S

/cm

.K)

1000/T (K-1)

Ea = 9.1 X 10

-2 eV

Figure 5.61: Arrhenius Plot from DC conductivity Data at Air Atmosphere

1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8

7.8

8.0

8.2

8.4

8.6

8.8

9.0

9.2

1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.97.4

7.6

7.8

8.0

8.2

8.4

8.6

8.8

9.0

9.2

ln

σσ σσT

(S/c

m.K

)

1000/T (K-1)

Ea = 9.9 X 10

-2 eV

Linear fit

Linear Fit Data

Arhenius plot at H2 Atmosphere

Ea = 9.9 X 10

-2 eV

ln σσ σσ

T (

S/c

m.K

)

1000/T (K-1)

Figure 5.62: Arrhenius Plot from DC Conductivity Data at H2 Atmosphere


167


The AC Electrochemical Impedance Spectroscopy was carried out in a

frequency range of 0.01 Hz to 1 MHz over temperature range of 500-600oC. The

experimental data and results are shown in Figure 5.63. It can be seen from the Figure

5.63 that the resistance of the material gradually increases with decrease of

temperature. It possesses the highest value of resistance at 300oC. The impedance

spectra in the Figure 5.63 give information about the distribution of resistance over

the frequency range. The semicircles in the figure show the impedance at higher

frequency range and the linear line shows the impedance at lower frequency.

However, at lower frequencies, resistances are high due to the contribution of wires,

leads and sample holder etc. For this reason, AC impedance spectra show the high

resistance comparative to resistance found during DC conductivity measurements of

the same material.

8 12 16 20 24 28 32-2

0

2

4

6

8

Zim

(ΩΩ ΩΩ

)

Zre

(ΩΩΩΩ)

T600oC

T550oC

T500oC

AIR Atmosphere

Figure 5.63: AC Electrochemical Impedance Spectroscopy of LSCZ Cathode


168


The LSCZ material has been used as cathode material and its performance has

been studied with BCFZ and conventional Ni based anode as well as NKCDC and

conventional NSDC electrolytes. For this purpose, four different types of fuel cell

were constructed. The fuel cells were fabricated in consecutive three layers of

Composite Anode/Electrolyte/Composite Cathode as discussed below:

a) BCFZ-NKCDC/NKCDC/LSCZ-NKCDC

b) BCFZ-NSDC/NSDC/LSCZ-NSDC

c) Ni-NKCDC/NKCDC/LSCZ-NKCDC

d) Ni-NSDC/NSDC/LSCZ-NSDC

The performance of this cathode material was measured in the temperature

range of 400-500oC. The results of measurements are shown in Figure 5.64(a-d) and

listed in Table 5.22. The values of open circuit voltage, current densities were

measured by the experiment using fuel cell testing unit L-43, China. Hydrogen was

fed as a fuel at anode side at a rate of 100ml/min and air as oxidant at cathode side

during experiment.


169

0 200 400 600 800 1000 1200 14000.0

0.2

0.4

0.6

0.8

1.0

1.2

0

100

200

300

400

500

Po

wer

Den

sity

(m

W/c

m2)

Volt

age (

V)


T550oC

T500oC

T450oC

(a)

Figure 5.64(a): Performance of Fuel Cell using BCFZ-5-NKCDC Anode, NKCDC

Electrolyte and LSCZ-NKCDC Cathode

0 200 400 600 800 1000 1200 14000.0

0.2

0.4

0.6

0.8

1.0

1.2

0

50

100

150

200

250

300

350

Volt

ag

e (V

)


T550oC

T500oC

T450oC(b)

Po

wer

Den

sity

(m

W/c

m2)

Figure 5.64(b): Performance of Fuel Cell using BCFZ-5-NSDC Anode, NSDC

Electrolyte and LSCZ-NSDC Cathode


170

0 400 800 1200 1600 20000.0

0.2

0.4

0.6

0.8

1.0

1.2

0

100

200

300

400

500

600

Po

wer

Den

sity

(m

W/c

m2)

Vo

ltage (

V)


T550 T550 T550

(c)

Figure 5.64(c): Performance of Fuel Cell using Ni-NKCDC Anode, NKCDC

Electrolyte and LSCZ-NKCDC Cathode

0 500 1000 1500 2000 25000.0

0.2

0.4

0.6

0.8

1.0

1.2

0

200

400

600

800

1000

Po

wer

Den

sity

(m

W/c

m2)

Volt

ag

e (V

)


T 550oC

T 500oC

T 450oC

(d)

Figure 5.64(d): Performance of Fuel Cell using Ni-NSDC Anode, NSDC

Electrolyte and LSCZ-NSDC Cathode


171

Table 5.22: Fuel Cell Performance Data Based on LSCZ Cathode Material

Cell

Category


anode electrolyte Cathode OCV

(V)

Current Density

mA/cm2)

Power Density

(mW /cm2)

LSCZ (a) BCFZ NKCDC LSCZ 1.016 1257.812 334.917

LSCZ (b) BCFZ NSDC LSCZ 0.9 1078.125 440.344

LSCZ (c) Ni- NKCDC LSCZ 0.995 1803.125 545.40

LSCZ (d) Ni NSDC LSCZ 1.02 2250 850.786

5.9.10 Cost Analysis

The cost analysis has been done for this LSCZ cathode material for solid oxide

fuel cell and it has been found that LSCZ cathode maintained open circuit voltage,

power density with hydrogen (fuel) and air (oxidant) at comparatively low

temperature of 550oC. This is an alternative electrode having prominent potential as a

cathode, which has specified a competitive alternative candidate to replace the

conventional cathodes LSN, LN and LSCF available at Sigma Aldrich. Rather than its

cost has been found the most cheap in all aspects including raw materials, shipment,

power costs, laboratory cost, researcher salaries and others. The present estimated

ground cost has been calculated 125€/20 grams fine powder and its cost can be further

reduced by large scale manufacturing. The cost of above mentioned LSN, LN and

LSCF cathodes has been noticed as 213.5€/20 gram, 213.50€/20 gram and

132€/20gram on Sigma Aldrich website. The present cost of LSCZ cathode powder

elucidate that the LSCZ cathode is almost less than 50% cheap than that of

conventional LSN as well as LSN and little less than that of LSCF cathode

respectively. The evaluated cost of this electrode has been illustrated in Table 5.23;


172

Table 5.23: Estimated Cost of LSCZ Electrode (La0.1Sr0.9Co0.2Zn0.8)


La(NO3)3.6H2O 7.00 36.89 4708.20

Sr(NO3)2 25.60 314.368 40122.90

Co(NO3)2.6H2O 8.10 13.867 1769.875

ZnCO3 59.30 4.47 570.507

BFTZ Total Cost / 100g 369.595 47171

Sintering Present Charges 10 Commercial Units 2.00 260

Labor Cost Researcher per day Salary 8 1050


Total Cost After sintering G. T / 60 gram 380 48526

5.9.11 CONCLUSIONS

La0.6Sr0.4Co0.3Zn0.7 composition synthesized by wet chemical method

possesses cubic pervoskite structure.

Zn compound has been used in cathode material, which executes reliable

performance.

This can be an alternative of LSCF, BSCF, LSM, LSN and LN electrode

materials and it has been noticed that the prepared cathode LSCZ material is

cheaper than that of above cathode materials reported at Sigma Aldrich.

A four hours sintering at 800oC produces good crsytallinity.

LSCZ cathode material has electronic conductivity of 20 and 4.88 S/cm at

600oC in air and hydrogen atmosphere, respectively.

The prepared cathode material has area specific resistance of 0.03-0.63

Ω.cm2when the temperature falls from 600-300oC.

The maximum value of OCV and power density was found to be 1.02V and

850.79mW/cm2 at temperature 550oC, respectively.

Chapter No. 5 Results and Discussion Discussion

173

5.10 DISCUSSION

5.10.1 Fuel Cell Fabrication

Basically, a fuel cell has three things; electrodes (anode and cathode),

electrolyte, and the fuel (any material that can provide oxygen and hydrogen: water,

ethanol etc.). In the early days of the proton exchange membrane fuel cell research

platinum was used as a catalyst. These platinum catalysts are coated on carbon layer

or PTFE tape. The platinum is costly metal and works with pure hydrogenonly. A lot

of research work has been done to reduce the cost of fuel cell. Literature survey

indicates that the replacement of ‘Pt catalyst’ by its alloy or some other suitable

material may be a positive approach for reducing the cost of fuel cells. Alternatively

one may look for other system(s) which could be employed as fuel cell. One such

approach is the development of Solid Oxide Fuel Cell (SOFC) which do not require Pt

catalyst and is also relatively cheap.

The solid oxide fuel cells (SOFCs) utilize Ni-YSZ cermet as electrodes and

Yttria Stablized Zirconia (YSZ) as electrolyte. This fuel cell operates at 1000oC.The

electrode consists of a costlymaterial (Ni-YSZ cermet) but still its cost is much less

than the one which uses Pt as a catalyst. Moreover, it requires high

manufacturing/sinteringtemperature (1600oC) and takes a long time (8 hours) for its

preparation. Additionally, the cost of electrolyte material YSZ is also high. Due to

high cost of raw materials and elevated manufacturing temperature as well as high

working temperature, the cost of solid oxide fuel cell is too high to make it a

commercial device.

In order to find a viable and low cost fuel cell that may be fabricated and be

workable at comparatively low temperature, one needs to find alternate solutions. For

this purpose, following approaches were implemented in the present study;

Chapter No.5 Results and Discussion Discussion

174

I. Identification and use of cheap raw material

II. Lowering of sintering temperature

III. Reduction of sintering time

IV. Lowering of operating/working temperature

In the present work, Zn compound were identified to replace Ni-YSZ

components to produce a cheap fuel cell having low manufacturing, working and

operating temperature. The Zn compounds have numerous characteristics (as

discussed in section ) that make it a suitable candidate for the development of low

cost fuel cell.

In view of above approaches, commercially available chemicals (see experimental

section) were identified and used to prepare cheap electrodes and electrolytes. The

proposed electrodes (CNZGC, ANZ, CMZ, BCFZ, BFTZ, BSCM, LSCZ) and

electrolytes (NK-CDC, Y-GDC, NSDC, and GDC) were prepared atrelatively low

sintering temperature (800oC) and that too in much smaller time (4 hrs). They fulfill

all the fundamental conditions of a fuel cell in terms of electronic/ionic conductivity

as well as performance with the advantage of working at comparatively low

temperature (300-600oC).

It can be seen that majority of the new electrodes are based on zinc compounds. The

price comparison as based on present rates indicates that Zn(NO3)2.6H2O is 25 times

cheaper than Ni Ni(NO)2.6H2O(Annexure 4 on page XXVI).

Many Zn based electrodeswere developed to replace Ni-YSZ cermet electrode. A

complete list of these electrodes is available on pages 63-65.Experimental studies of

these electrodes have pointed out that the performance of fuel cell utilizing BCFZ-5

as anode, NKCDC as electrolyte, and LSCZ as cathode is the best amongst the whole

lot and at the same time comparable to Ni-YSZ cermet based fuel cell which make


175

use of expensive electrodes as compare to newly developed electrodes employed in

the present study.

Table 5.24: Comparative Cost Analysis of Electrode Materials

Sr. No.

Cost of Electrodes Prepared and reported in this thesis

Cost

Cost of Conventional Electrodes available from Sigma Aldrich

Cost

Anode/Cathode

Name of Electrode wt. (g)

€ PKR Name of Electrode wt. (g)

€ PKR

1 Anode CNZGC (Dry-7) 10 32.50 4125

NiO 10 65

2 Anode ANZ 44(b) 10 17.50 2275 3 Anode CMZ 10 20.00 2550 4 Anode BCFZ-5 10 15 1900 5 Anode BFTZ 10 12.50 1620

6 Cathode LSCZ 10 62.50 8000

LSN (La1.4Sr0.4NiO4) 10 106 13800 LN (La2NiO4) 10 106 13800 LSCF (La0.6Sr0.4Co0.2Fe0.8O3)

10 65 8450

7 Composite Anode

BCFZ-NKCDC (80wt.%:20wt.%)

10 16 2030 Ni-YSZ (60wt%:40wt%)

10 28.70 3719

8 Composite Cathode

LSCZ-NKCDC (80wt.%:20wt.%)

10 56 7250 LSCF/GDC (50:50) 10 56 7250

The overall cost of the fuel cell is further reduced by using newly developed cheap

electrolyte (NKCDC) and cathode (LSCZ) materials. It may be noted that the new

electrolyte material uses calcium compound as a major component and the cost of

calcium compound is much less than that of samarium and gadolinium compounds

(see Annexure 4 on page XXVI)as used in already reported electrolyte materials for

SOFC.

Table 5.25: Comparative Cost Analysis of Electrolyte Materials

Sr. No.

Cost of Electrolyte Prepared and reported in this thesis

Cost

Cost of Conventional Electrolyte available from Sigma Aldrich

Cost

Name of Electrolyte

wt.(g) € PKR Name of Electrolyte

wt.(g) € PKR

1 NK-CDC 10 20.00 2550 YSZ 10 92.00 11680


176

An overall cost comparison of electrodes and electrolyte used in the present

study is provided in Table 5.24 and 5.25. It can be noted that the newly developed

electrode and electrolyte materials are much cheaper than conventionally used

electrode (Ni-YSZ) and electrolytes (YSZ, SDC, and GDC).

With the implementation of above approaches, the cost of the SOFC has been

sufficiently reduced and it seems to be possible to produce and use these cells on

commercial scale.

“From the above discussion, it can be concluded that the

objective of developing low cost electrodes for fuel cells has been

successfully achieved in the present circumstances”

Chapter No. 5 Results and Discussion References

177

References

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[2] Zhu, B., International Journal of Energy Research, Vol. 30, Issue 11, (2006);

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[3] Xia, C., Li, Y., Tian, Y., Liu, Q., Wang, Z., Jia, L., Zhao, Y. and Li, Y.,

Journal of Power Sources, Vo. 195, Issue 10, (2010); Pages: 3149–3154.

[4] Raza, R., Wang, X., Ma, Y., Lia, X. and Zhu, B., International Journal of

Hydrogen Energy, vol. 35, Issue 7, (2010); Pages: 2684-2688.

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[8] Leng, Y. J. and Chan, S. H., Solid State Letters, Vol. 9, Issue 2, (2006); Pages:

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[9] Raze, R., Wang, X., Ma, Y., Huang, Y. Z. and Zhu, B., Journal of Nano

Research, Vol. 6,(2009); Pages: 197-203.

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Energy, Vol.35, Issue 7, (2010): Pages: 2684 – 2688.

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Acta, Vol. 47, Issue 13-14, (2002); Pages: 2183-2188.

[12] Kharton, V. V., Tsipis, E. V., Marozau, I. P., Viskup, A. P., Frade, J. R. and

Irvine, J. T. S., Solid State Ionics 178 (2007) 101–113.

[13] Raza, R., Wang, X., Ma, Y. and Zhu, B., Journal of Power Sources, Vol. 195,

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Issue 2, (2009); Pages: 128-138.

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[16] Sun, X., Li, S., Sun, J., Liu, X. and Zhu, B., International Journal of

Electrochemical Science, Vol. 2, Issue (2007); Pages: 462-468.

[17] Darab, M., Toprac, M. S., Syvertsun, E., G. and Muhammad, M., Journal of

the Electrochemical Society, Vol. 156, Issue 8, 92009); Pages: K139-K143.

[18] Shao, Z. and Haile, S. M., Nature, Vol. 431, (2004); Pages: 170-173.

[19] Toprac, M. S., Darab, M., Syvertsun, E. G. and Muhammad, M., International

Journal of Power Sources, Vol. 35, Issue 17, (2010), Pages: 9448-9454.

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Chapter No. 6

Chapter No. 6 Summary, Conclusions and Recommendations

180

6 Summary, Conclusions and Recommendations

6.1 Summary

The main objective of this study was to prepare low cost electrodes for solid

oxide fuel cells. For this purpose, a number of electrode materials were prepared.

Among these materials, only seven electrodes (five anodes and two cathodes) with

different compositions were selected. The structures of the prepared samples have

been determined by indexing all the peaks from XRD patterns using Jade-5 software.

The particle sizes were calculated by applying Scherer’s formula (XRD) and scanning

electron microscopy (SEM) analysis. The particle size as obtained with both the

techniques were in the range of 10-80nm. The electrochemical properties were also

studied.

The conductivity measurements exhibited a maximum conductivity of 25.84

S/cm at 600oC for Ba0.05Cu0.25Fe0.10Zn0.60 (BCFZ-5) electrode/anode under hydrogen

atmosphere. The BSCM (Ba0.2Sr0.8Co0.3Mn0.7) cathode showed a maximum

conductivity of 37 S/cm at 600oC at air atmosphere.

NK-CDC cubic fluorite structured electrolyte possesses an ionic conductivity

of 0.1 S/cm at 600oC under air atmosphere. The structure and ionic conductivity of

NK-CDC has been found same as that for conventional electrolytes like NSD,

NKSDC and GDC etc. The performance of these all the electrode and electrolyte

materials was measured by providing hydrogen as a fuel at anode side and air as

oxidant at cathode side in the temperature range of 400-550oC. The open circuit

voltage and current were recorded and I-V, I-P characteristics were drawn. The active

area of fuel cell was 0.64 cm2 during the measurements. Among these electrodes,

BCFZ-5 electrode/anode has been found more compatible for NKCDC electrolyte

having an excellent performance of 741.87mW/cm2 for symmetric fuel cell, while for


181

non-symmetric, it exhibited 933.41mW/cm2 with BSCF cathode. However, the

BCFZ-5 anode has also been tested with other cathodes and a comparative chart of its

performance is shown in Table 6.1.

Table 6.1: Comparative Chart of Performance of BCFZ-5 Anode Sample

Category

Fuel Cell Components Fuel Cell Performance at 550oC Status of the fuel cell

Composite

Anode

Composite

Electrolyte

Composite

Cathode

Max.

OCV (V)

Max. C.D.

(mA/cm2)

Max. P.D.

(mW/cm2)

BCFZ-5 BCFZ-5 NKCDC BCFZ-5 1.007 2260.789 741.87 Symmetric

BCFZ-5 BCFZ-5- NKCDC BSCF 1.07 2328.125 933.406 Asymmetric

BCFZ-5 BCFZ-5 NKCDC SBCM 1.01 1504.6785 525.2438 Asymmetric

BCFZ-5 BCFZ-5 NKCDC LSCZ 1.02 1257.812 334.917 Asymmetric

6.2 CONCLUSIONS

The new electrodes have following characteristics:

Novel Zn based electrodes has been fabricated by solid state reaction method

and wet chemical method with the particle size smaller than 100 nm.

Nanocomposite approach has been successfully applied to synthesize the

electrode materials with enhanced electronic conductivity in temperature range

of 300-600oC.

BCFZ electrodes based on Zn (NO3)3.6H2O as major chemical compound has

been found to be cheaper than Ni-cermets electrode.

It requires comparatively low temperature (800oC) for its preparation, while

Ni-cermets anode requires more than 1000oC for its preparation.

It requires a sintering time of four hours only, while Ni-cermets anode needs

more than ten hours sintering.

This means proposed materials are most effective in term of their preparation.

A comparison of all the prepared materials is provided in Tables 6.2 and 6.3

which shows that BCFZ-5 anode alongwith NK-CDC electrolyte and BSCF cathode

is the best arrangement for making a durable and cost effective solid oxide fuel cell.


182

Table 6.2: Comparative Chart of Particle Size, Electrical Conductivity and Activation Energy of All the Samples

Cell Category

Sintering Temp. (oC)

Particle Size (nm)

DCConductivity (S/cm) at 600oC

AC Conductivity (S/cm) at 600oC

Ea (eV) from DC σ 300-600oC

Ea (eV) from AC σ 300-600oC

Status of Material

At H2 At Air At H2 At Air At H2 At Air At H2 At Air

Dry-1 800oC 41.33 0.23 0.20 - - 0.32 - - - Anode Dry-3 800oC 75.39 0.29 0.11 - - 0.35 - - - Anode Dry-5 800oC 70.21 0.11 0.09 - - 0.16 - - - Anode Dry-7 700oC 37.06 - - - - - - - - Anode Dry-7 800oC 20.69 4.14 1.76 - - 0.04 - - - Anode Dry-7 900oC 20.46 - - - - - - - - Anode Dry-7 1000oC 21.02 - - - - - - - - Anode Dry-9 800oC 57.08 0.12 0.10 - - 0.23 - - - Anode 44 (a) 800oC 34.55 2.80 - 1.39 - 5.9x10-2 - 7.3x10-2 - Anode 44 (b) 800oC 50.21 10.84 - 4.88 - 2.7x10-2 - 9.6 x10-2 - Anode 44 (c) 800oC 24.70 0.90 - 0.96 - 4.9x10-2 - 7.6 x10-2 - Anode 44 (d) 800oC 24.57 1.31 - 1.54 - 4.4x10-2 - 8.3 x10-2 - Anode 44 (e) 800oC 31.10 0.79 - 0.85 - 3.1x10-2 - 8.0 x10-2 - Anode CMZ 800oC 31.50 5.79 2.73 - - 6.0x10-2 - - - Electrode

BCFZ-1 800oC 58.16 0.86 0.84 - - 2.3x10-2 25.0x10-2 - - Electrode BCFZ-2 800oC 35.86 1.94 1.20 - - 1.2x10-2 14.1x10-2 - - Electrode BCFZ-3 800oC 56.84 4.55 3.00 - - 8.6x10-2 14.3x10-2 - - Electrode BCFZ-4 800oC 38.46 6.14 4.15 - - 8.3x10-2 8.1x10-2 - - Electrode BCFZ-5 800oC 25.28 25.84 5.50 - - 7.1x10-2 8.1x10-2 - - Electrode/Anode BCFZ-6 800oC 31.79 1.31 0.09 - - 12.3x10-2 11.1x10-2 - - Electrode BFTZ 800oC 39.17 5.86 - 4.81 - 0.15 - 0.14 - Anode

NKCDC 800oC 12 - - 0.02 0.10 - - 0.52 0.20 Electrolyte GDC-Y2O3 750oC 22 - - 0.06 0.12 - - - 0.27 Electrolyte

BSCM 800oC 49.09 17 37 4.18 6.94 0.46 0.49 - - Cathode LSCZ 800oC 47.55 4.78 20.29 6.67 9.92 9.9x10-2 9.1x10-2 - - Cathode


183

Table 6.3: Fuel Cell Performance Data of All the Fuel Cells Cell Category with

Sintering Temperature

Fuel Cell Construction Fuel Cell Performance at 550oC Status of the Solid Oxide Fuel Cells Anode Electrolyte Cathode OCV

(V) C.D.(mA/cm2) P.D. (mW/cm2)

Dry-1 (800oC) CNZGC NKSDC BSCF 0.825 1542.19 478 Asymmetrical



Dry-7 (800oC) CNZGC NKSDC BSCF 1.025 1875 570 Asymmetrical

Dry-9 (800oC) CNZGC NKSDC BSCF 1 1312.5 554 Asymmetrical

Dry-7 (700oC) CNZGC NKSDC BSCF 0.7 110.94 256.38 Asymmetrical

Dry-7 (900oC) CNZGC NKSDC BSCF 0.73 2246.56 551.25 Asymmetrical


44(a) (800oC) ANZ NKSDC BSCF 0.965 991.25 303.28 Asymmetrical

44(b) (800oC) ANZ NKSDC BSCF 1.030 1725 705.56 Asymmetrical

44(c) (800oC) ANZ NKSDC BSCF 0.908 503.125 139.5 Asymmetrical

44(d) (800oC) ANZ NKSDC BSCF 0.875 1003.125 296.48 Asymmetrical

44(e) (800oC) ANZ NKSDC BSCF 0.760 801.562 171.94 Asymmetrical

CMZ (800oC) CMZ NSDC CMZ 1.124 2031.25 728.86 Symmetrical

BCFZ-1 800oC) BCFZ-1 NKCDC BCFZ-1 0.95 172 40.30 Symmetrical

BCFZ-2(800oC) BCFZ-2 NKCDC BCFZ-2 0.98 1517.028 468.11 Symmetrical


BCFZ-4(800oC) BCFZ-4 NKCDC BCFZ-4 0.97 1857 545.82 Symmetrical



BCFZ-5(800oC) BCFZ-5 NKCDC BSCF 1.07 2328.125 933.41 Asymmetrical

BFTZ (800oC) BFTZ NKCDC BSCF 0.910 585.94 126.81 Asymmetrical

BFTZ (800oC) BFTZ NSDC BSCF 0.950 1550 470.62 Asymmetrical

NK-CDC (700oC) NiO NKCDC NiO 1.0 1726 567 Symmetrical

Y-GDC-(750oC) NiO Y-GDC Li-NiO 1 2200 785 Symmetrical

BSCM-a (800oC) BCFZ NKCDC BSCM 1.01 1504.678 525.2437 Asymmetrical

BSCM-b (800oC) BCFZ NSDC SBCM 1.15 1448.437 549.2953 Asymmetrical

BSCM-c (800oC) NiO NKCDC SBCM 1.02 2239.062 725.987 Asymmetrical

BSCM-d (800oC) NiO NSDC SBCM 1.002 1800 743.375 Asymmetrical

LSCZ-a (800oC) BCFZ NKCDC LSCZ 1.016 1257.812 334.917 Asymmetrical

LSCZ-b (800oC) BCFZ NSDC LSCZ 0.9 1078.125 440.344 Asymmetrical

LSCZ-c (800oC) NiO NKCDC LSCZ 0.995 1803.125 545.40 Asymmetrical

LSCZ-d (800oC) NiO NSDC LSCZ 1.02 2250 850.786 Asymmetrical


184

The choice of Zn material for the preparation of electrodes instead of Ni along

with calcium doped ceria based electrolytes is based on its capacity to perform

reduction and catalytic activity at anode under hydrogen atmosphere as well as

oxidation at cathode under air atmosphere. The alternate materials; Zn(NO3)2.6H2O

and Ca(NO3)2.4H2O instead of NiNO3 and Sm(NO3)3.6H2O or Gd(NO3)3.6H2O make

the solid oxide fuel cell more cheaper by an average factor of 25 in addition to

lowering of its manufacturing as well as working temperature.

The thesis involves development of new and cheaper materials for anode, cathode

and electrolyte of solid oxide fuel cells. The work concerns materials to reduce

operating temperature of solid oxide fuel cell from 800-1000oC to below 600oC.

Thus it will be possible to reduce cost of SOFC systems which is considered to one

the main obstacle on the commercialization.

It is believed that the proposed solid oxide fuel cell, which works at low

temperature (400-550oC) have a great potential to reduce the cost of cell fabrication

with an additional advantage of its life improvement. The present work provides a

promising and valuable solution to promote the fuel cell technology on commercial

basis.

In view of highly consumption of fossil fuels, the present resources of fossil fuels

are going to be end. The cost is also increasing due to limited and reserved resources.

If the use of fossil fuels would not be controlled, then, it may be possible the world has

to face a lot of problems in coming century. Therefore, the REVOLUTION of FUEL

CELL Technology is a mandatory action. The primarily research work on fuel cell

technology may be proved a fruitful precursor of fuel cell revolution.

Particularly, our country Pakistan is highly deserved candidate to take initiative

step to launch fuel cell technology in all over the country.


185

6.3 Further Recommendations

Following suggestions/recommendations may improve the cell performance.

1) The performance of the electrode materials may be tested with the

presence of other hydrocarbon fuels for testing stability.

2) Composite electrodes should be prepared with an addition of ceria

composite electrolyte during manufacturing process to see if it could

further improve the performance of the cell.

3) Some other electrolytes having nano structure may be developed and

tested to see if they could improve the cell performance.

4) Enhancement in conductivity, improvement of catalytic properties and

long-term stability need further investigation.

5) A cyclic (regenerative) fuel cell system capable of producing hydrogen

from water electrolysis using solar energy may help building cheaper

power stations and also realize a cheaper source of renewable energy.

6) New cheap material of TiO2 is under interest and work based on this

material will be extended in future.

7) Single component solid oxide fuel cell is under development; three in one

is a new development.

ANNEXURE 1

XXIII

ANNEXURE-1

Ghazanfar Abbas, Rizwan Raza, M, Ashraf Chaudhry, Bin Zhu. “Study

of CuNiZnGdCe Nanocomposite Anode for Low Temperature SOFC.”

Nanoscience and Nanotechnology Letters, Vol. 4 (2012), Pages 389-393.

ANNEXURE 2

XXIV

ANNEXURE-2 Ghazanfar Abbas, Rizwan Raza, M. Ashraf Chaudhry, Bin Zhu,

“Preparation and Characterization of Nanocomposite Calcium Doped

Ceria Electrolyte with Alkali Carbonates (NK-CDC) for SOFC.” Journal

of Fuel Cell Science and Technology, Vol. 8, Issue 4, Pages 041013.

ANNEXURE 3

XXV

ANNEXURE-3

Rizwan Raza, Ghazanfar Abbas, S. Khalid Imran, Imran Petal, Bin

Zhu, “GDC-Y2O3 Oxide Based Two Phase Nanocomposite

Electrolyte.” Journal of Fuel Cell Science and Technology, Vol. 8,

Issue 4, Pages 041012.

ANNEXURE 4

XXVI

ANNEXURE-4

Prices Chart of Major Chemicals Used in this Work (Aldrich-Sigma) Sr.

No.

Chemical

Formula

Purity CAS

Number

Wt.

(gm)

Prices: Dated: June 24, 2011

SEKa $b PKRb

1 Ni(NO3)2.6H2O ≥ 98.5 % 13478-00-7 50 760.73 117.17 10063.69

2 Zn(NO3)2.6H2O ≥ 99.0 % 10196-18-6 500 283.59 43.68 3751.61

3 Ce(NO3)3.6H2O 99% 10294-41-4 100 370.53 57.08 4901.36

4 Ca(NO3)2.6H2O ≥ 99.0 % 13477-34-4 500 525.78 80.99 6955.62

5 Sm(NO3)3.6H2O ≥ 98 % 13759-83-6 50 1888.88 290.99 24988.26

6 Gd(NO3)3.6H2O 99.9% 19598-90-4 100 1888.88 290.99 24988.26

ahttp://www.sigmaaldrich.com Dated: June 24, 2011

bhttp://www.xe.com/ucc/ Dated: June 24, 2011

SEK: Swedish Krona $: Dollar PKR: Pakistani Rupee

ANNEXURE 5

XXVII

ANNEXURE-5 XRD Chart of CNZGC Anode Material

Cu0.13Ni0.24Zn0.32Ce0.19Gd0.12 2θ d(A) FWHM

Preparation Method: Solid State Reaction

22.078 23.982 28.334 29.898 31.446 31.717 32.533 34.387 35.202 35.525 36.206 37.259 38.755 40.110 41.290 42.291 42.700 45.113 46.152 46.538 47.510 48.632 49.873 50.792 51.438 51.931 52.337 53.273 53.597 54.039 55.229 56.061 56.554 58.119 58.867 59.478 60.652 61.587 62.181 62.845 65.752 66.209 66.992 67.927 69.050 69.747 70.291 71.176 71.585 72.212 72.703 73.536 74.320 74.694 76.513 76.972 77.923 78.434 79.029

4.0228 3.7076 3.1472 2.9861 2.8425 2.8188 2.7499 2.6058 2.5473 2.5249 2.4790 2.4113 2.3216 2.2462 2.1847 2.1353 2.1158 2.0080 1.9653 1.9498 1.9122 1.8706 1.8270 1.7961 1.7750 1.7593 1.7466 1.7181 1.7085 1.6955 1.6618 1.6391 1.6260 1.5859 1.5675 1.5528 1.5255 1.5046 1.4917 1.4775 1.4190 1.4103 1.3957 1.3788 1.3591 1.3472 1.3381 1.3236 1.3171 1.3072 1.2995 1.2868 1.2752 1.2698 1.2440 1.2377 1.2250 1.2183 1.2106

0.281 0.279 0.395 0.410 0.277 0.346 0.314 0.191 0.532 0.435 0.179 0.244 0.269 0.137 0.109 0.072 0.157 0.303 0.195 0.213 0.205 0.220 0.207 0.336 0.209 0.161 0.112 0.602 0.211 0.113 0.465 0.359 0.280 0.319 0.248 0.205 0.119 0.264 0.378 0.247 0.499 0.692 0.119 0.286 0.231 0.120 0.420 0.132 0.114 0.569 0.706 0.408 0.912 0.470 0.205 0.299 0.152 0.110 0.458

Produced at 800oC Sintering Time = 4 hour Cu-Kα ; λ = 1.5408 Å System: Three phases NiO Based Card No. 44-1159

NiZnO Based Card No. 47-1019

GDC Based Card No. 46-0508

Rhombohedral System a: 2.955 Å b: 2.955 Å c: 2.995 Å α: ≠ 90o

β: ≠ 90o γ: ≠ 90o

V: 54.66 M(wt.): 74.70 Ρ(m): 7.75 Å Z: 3 Space Group: R-3m(166)

Orthorhombic System a: 33.326 Å b: 8.869 Å c: 12.449 Å α: 90o

β: 90o γ: 90o

V: 3694.31 M(wt.): 254.84 Ρ(m): 7.69 Å Z: 69 Space Group: Ab2m (39)

Cubic Fluorite System a: 10.858 Å b: 10.858 Å c: 10.858 Å α: 90o

β: 90o γ: 90o

V: 279.98 M(wt.): 351.99 Ρ(m): 8.57 Å Z: 16 Space Group: La-3(206)

ANNEXURE 6

XXVIII

ANNEXURE-6 XRD Chart of ANZ(44b) Anode Powder

Al0.10Ni0.20Zn0.70 2θ d(A) FWHM


31.138 31.734 32.484 34.403 35.524 36.207 36.937 38.720 42.938 47.527 48.666 51.451 53.514 56.588 58.237 59.239 59.446 62.369 62.860 65.085 65.320 65.855 66.312 67.895 69.035 72.350 74.779 76.869 78.706

2.8699 2.8173 2.7540 2.6046 2.5250 2.4789 2.4316 2.3236 2.1046 1.9115 1.8694 1.7746 1.7110 1.6251 1.5829 1.5585 1.5536 1.4876 1.4772 1.4319 1.4274 1.4171 1.4084 1.3794 1.3593 1.3050 1.2685 1.2392 1.2148

0.458 0.245 0.153 0.201 0.164 0.317 0.243 0.348 0.228 0.240 0.259 0.291 0.304 0.224 0.398 0.449 0.508 0.396 0.244 0.416 1.080 0.374 0.364 0.261 0.379 0.527 0.446 0.381 0.410

Produced at 800oC Sintering Time = 4 hour Cu-Kα; λ = 1.5408 Å System: Two phases ZnO Based: Card No. 36-1451

NiO Based: Card No. 65-2901

Hexagonal System a: 3.250 Å b: 3.250 Å c: 5.07 Å α: 90o

β: 90o γ: 120o

V: 47.62 M(wt.): 81.38 Ρ(m): 6.43Å Z: 2 Space Group: P63mc(186)

Cubic System a: 4.195 Å b: 4.195 Å c: 4.195 Å α: 90o

β: 90o γ: 90o

V: 73.80 M(wt.): 74.70 Ρ(m): 7.75Å Z: 4 Space Group: Fm-3m(255)

ANNEXURE 7

XXIX

ANNEXURE-7 XRD Chart of CMZ Anode Material

Al0.10Ni0.20Zn0.70 2θ d(A) FWHM


18.372 30.255 31.735 32.533 34.404 35.577 36.223 37.277 38.739 43.345 47.511 48.650 53.698 56.555 57.387 58.170 61.536 62.845 66.092 67.927 69.050 72.280 74.438 74.966 75.272 76.904

4.8252 2.9516 2.8173 2.7500 2.6046 2.5214 2.4779 2.4102 2.3225 2.0858 1.9122 1.8700 1.7055 1.6260 1.6043 1.5846 1.5057 1.4775 1.4126 1.3788 1.3591 1.3061 1.2735 1.2658 1.2614 1.2387

0.322 0.270 0.168 0.226 0.165 0.324 0.180 0.231 0.248 0.480 0.220 0.280 0.397 0.203 0.413 0.232 0.276 0.358 0.483 0.355 0.256 0.499 0.682 1.037 0.803 0.362

Produced at 800oC Sintering Time = 4 hour Cu-Kα λ = 1.5408 Å System: Two phases ZnO Based: Card No. 36-1451

CuMnO Based: Card No. 65-2901


β: 90o γ: 120o


Cubic System a: 8.274Å b: 8.274Å c: 8.274Å α: 90o

β: 90o γ: 90o

V: 566.43 M(wt.): 241.72 Ρ(m): 5.73Å Z: 4 Space Group: F

ANNEXURE 8

XXX

ANNEXURE-8 XRD Chart of BCFZ Electrode/Anode Materials

Ba0.05Cu0.25Fe0.10Zn0.60 2θ d(A) FWHM


23.898 24.203 27.379 27.687 30.905 31.764 32.628 33.378 33.540 34.133 34.436 35.575 36.255 36.678 37.092 38.839 39.654 40.339 42.088 43.139 43.458 43.535 44.318 44.673 44.908 46.860 47.560 48.484 53.686 55.115 55.419 55.653 56.604 56.928 58.357 58.747 58.920 61.556 62.623 62.897 64.882 65.331 65.668 66.025 66.369 67.979 68.285 68.608 68.650 69.103 70.413 72.168 72.354 72.620 75.136 75.437 76.727 76.992 78.749 79.036

3.7204 3.6742 3.2548 3.2192 2.8910 2.8148 2.7421 2.6822 2.6697 2.6247 2.6022 2.5215 2.4758 2.4481 2.4218 2.3167 2.2710 2.2340 2.1451 2.0953 2.0806 2.0771 2.0422 2.0268 2.0167 1.9372 1.9103 1.8760 1.7059 1.6650 1.6566 1.6501 1.6246 1.6162 1.5800 1.5704 1.5662 1.5053 1.4822 1.4764 1.4359 1.4272 1.4206 1.4138 1.4073 1.3779 1.3724 1.3668 1.3660 1.3582 1.3361 1.3078 1.3049 1.3008 1.2634 1.2591 1.2411 1.2375 1.2142 1.2105

0.265 0.267 0.089 0.090 0.125 0.089 0.048 0.048 0.055 0.381 0.099 0.152 0.095 0.053 0.097 0.160 0.101 0.057 0.227 0.185 0.149 0.116 0.076 0.249 0.097 0.203 0.093 0.134 0.061 0.068 0.064 0.065 0.101 0.082 0.258 0.081 0.092 0.116 0.183 0.121 0.078 0.080 0.104 0.176 0.149 0.049 0.135 0.321 0.177 0.242 0.108 0.086 0.069 0.198 0.105 0.201 0.053 0.153 0.092 0.059

Produced at 800oC Sintering Time = 4 hour System: Single Phase ZnO Based: Card No. 36-1451 Hexagonal System a: 3.250 Å b: 3.250 Å c: 5.207 Å α: 90o

β: 90o γ: 120o

V: 47.62 M(wt.): 81.38 Ρ(m): 6.43 Å Z: 2 Space Group: P63mc(186)

ANNEXURE 9

XXXI

ANNEXURE-9 XRD Chart of BFTZ Anode Material

Ba0.15Fe0.10Ti0.15Zn0.60 2θ d(A) FWHM


22.078 23.982 28.334 29.898 31.446 31.717 32.533 34.387 35.202 35.525 36.206 37.259 38.755 40.110 41.290 42.291 42.700 45.113 46.152 46.538 47.510 48.632 49.873 50.792 51.438 51.931 52.337 53.273 53.597 54.039 55.229 56.061 56.554 58.119 58.867 59.478 60.652 61.587 62.181 62.845 65.752 66.209 66.992 67.927 69.050 69.747 70.291 71.176 71.585 72.212 72.703 73.536 74.320 74.694 76.513 76.972 77.923

4.0228 3.7076 3.1472 2.9861 2.8425 2.8188 2.7499 2.6058 2.5473 2.5249 2.4790 2.4113 2.3216 2.2462 2.1847 2.1353 2.1158 2.0080 1.9653 1.9498 1.9122 1.8706 1.8270 1.7961 1.7750 1.7593 1.7466 1.7181 1.7085 1.6955 1.6618 1.6391 1.6260 1.5859 1.5675 1.5528 1.5255 1.5046 1.4917 1.4775 1.4190 1.4103 1.3957 1.3788 1.3591 1.3472 1.3381 1.3236 1.3171 1.3072 1.2995 1.2868 1.2752 1.2698 1.2440 1.2377 1.2250

0.281 0.279 0.395 0.410 0.277 0.346 0.314 0.191 0.532 0.435 0.179 0.244 0.269 0.137 0.109 0.072 0.157 0.303 0.195 0.213 0.205 0.220 0.207 0.336 0.209 0.161 0.112 0.602 0.211 0.113 0.465 0.359 0.280 0.319 0.248 0.205 0.119 0.264 0.378 0.247 0.499 0.692 0.119 0.286 0.231 0.120 0.420 0.132 0.114 0.569 0.706 0.408 0.912 0.470 0.205 0.299 0.152

Produced at 800oC Sintering Time = 4 hour System: Two phase ZnO Based Card No. 36-1451

BaFeO3 Based Card No. 14-0180


β: 90o γ: 120o

V: 47.62 M(wt.): 81.38 Ρ(m): 6.34 Å Z: 2 Space Group: P63mc(186)

Cubic System a: 4.012 Å b: 4.012 Å c: 4.012 Å α: 90o

β: 90o γ: 90o

V: 64.58 M(wt.): 241.18 Ρ(m): 5.64Å Z: Space Group:

ANNEXURE 10

XXXII

ANNEXURE-10 XRD Chart of BSCM Cathode Material

Ba0.80Sr0.20C00.30Mn0.70 2θ d(A) FWHM

Preparation Method: Wet Chemical Method

20.191 21.430 25.070 25.869 27.518 28.095 28.691 29.471 31.513 32.363 33.981 34.299 35.014 36.493 37.000 37.733 38.638 39.436 41.271 42.257 43.006 43.412 44.008 44.739 46.932 47.253 47.629 48.239 48.677 49.535 49.840 50.551 52.967 53.425 53.833 54.493 55.007 55.398 56.096 57.678 58.969 59.514 60.448 60.856 61.194 61.826 62.369 62.846 63.202 63.539 64.152 64.578 65.225 65.921 66.211 67.723 68.233 68.607 68.948 69.289 69.864 70.558 71.872 72.314 72.689 73.317 73.760 74.116 74.472 75.339 76.716

4.394 4.143 3.549 3.441 3.238 3.173 3.108 3.028 2.836 2.636 2.612 2.560 2.460 2.427 2.382 2.328 2.283 2.185 2.136 2.101 2.082 2.055 2.024 1.934 1.922 1.907 1.885 1.869 1.838 1.828 1.804 1.727 1.713 1.701 1.682 1.668 1.657 1.638 1.608 1.596 1.565 1.552 1.530 1.520 1.513 1.499 1.487 1.477 1.470 1.463 1.450 1.442 1.429 1.415 1.410 1.382 1.373 1.366 1.360 1.355 1.345 1.333 1.312 1.305 1.299 1.290 1.283 1.278 1.273 1.260 1.241

0.194 0.563 0.307 0.515 0.659 0.786 0.259 0.135 0.357 0.328 0.291 0.312 0.322 0.470 1.395 1.057 0.162 0.089 0.607 0.213 0.931 0.703 0.227 0.386 0.139 0.888 0.511 0.077 0.172 0.517 0.485 0.087 0.556 0.604 0.104 0.244 0.476 0.465 0.417 0.088 0.197 0.177 0.112 0.139 0.169 0.111 0.076 0.220 0.240 0.267 0.343 0.119 0.298 0.647 0.382 0.249 0.317 0.297 0.127 0.078 0.200 0.068 0.718 0.642 0.913 0.159 0.120 0.109 0.110 0.202 0.206

Produced at 800oC Sintering Time = 4 hour Cu-Kα ; λ = 1.5408 Å System: Two phases BaMnO Based: Card No. 26-0169

BaCoO Based Card No. 52-1332

Monoclinic System a: 5.672 Å b: 4.782 Å c: 9.319 Å α: 90o

β: ≠ 90o γ: 90o

V: 259.64 M(wt.): 81.38 Ρ(m): 6.43Å Z: 4 Space Group: P63/mmc(194)


β: 90o γ: 120o

V: 551.09 M(wt.): 886.11 Ρ(m): 6.08Å Z: 2 Space Group: Fm-3m(255)

ANNEXURE 11

XXXIII

ANNEXURE-11 XRD Chart of the LSCZ Cathode Material

La0.10Sr0.90C00.20Zn0.80 2θ d(A) FWHM

Preparation Method: Wet Chemical Method

17.488 18.797 20.276 20.582 24.405 25.121 25.749 28.404 28.793 29.558 30.170 31.395 31.717 32.177 32.617 33.298 33.570 34.369 35.066 35.696 36.204 36.478 37.328 37.819 38.211 40.234 41.271 41.918 42.885 44.025 44.620 45.113 45.589 46.541 46.900 47.493 48.208 48.683 48.973 49.873 50.213 50.505 51.129 51.539 51.912 52.458 52.832 53.545 53.818 54.396 55.177 56.538 56.824 57.150 57.660 58.544 58.799 59.801 60.413 60.753 61.060 61.433 62.131 62.525 62.810 63.286 63.695 64.086 64.766 65.157 65.446 65.752 66.024 66.330 66.790 67.607 67.895 68.471 69.033 69.525 69.832 70.494 70.852 78.009 78.384 78.825 79.302

5.067 4.716 4.376 4.311 3.644 3.542 3.457 3.139 3.098 3.019 2.959 2.847 2.818 2.779 2.743 2.688 2.667 2.607 2.556 2.513 2.479 2.461 2.407 2.376 2.353 2.239 2.185 2.153 2.107 2.055 2.029 2.008 1.988 1.949 1.935 1.912 1.886 1.868 1.858 1.827 1.815 1.805 1.785 1.771 1.759 1.742 1.731 1.710 1.702 1.685 1.663 1.626 1.618 1.610 1.597 1.575 1.569 1.545 1.531 1.523 1.516 1.508 1.492 1.484 1.478 1.468 1.459 1.451 1.438 1.430 1.424 1.419 1.413 1.408 1.399 1.384 1.379 1.369 1.359 1.350 1.345 1.334 1.328 1.315 1.213 1.207 1.209

0.190 0.314 0.245 0.445 0.108 0.201 0.221 0.158 0.122 0.216 0.105 0.287 0.139 0.402 0.255 0.462 0.304 0.136 0.167 0.336 0.154 0.258 0.166 0.170 0.131 0.246 0.206 0.262 0.446 0.215 0.148 0.453 0.244 0.215 0.073 0.197 0.362 0.054 0.073 0.285 0.188 0.085 0.114 0.229 0.130 0.272 0.250 0.092 0.127 0.214 0.574 0.152 0.162 0.175 0.135 0.501 0.362 0.246 0.680 0.294 0.187 0.235 0.227 0.345 0.140 0.115 0.330 0.116 0.098 0.188 0.191 0.738 0.615 0.211 0.175 0.353 0.146 0.111 0.133 0.251 0.268 0.197 0.639 71.702 0.384 0.304 0.209

Produced at 800oC Sintering Time = 4 hour Cu-Kα; λ = 1.5408 Å System: Single Phases ZnO Based: Card No. 36-1451 Hexagonal Perovskite System a: 3.250 Å b: 3.250 Å c: 5.207 Å α: 90o

β: 90o γ: 120o


Abbreviations and Symbols

XXXIV

Abbreviations and Symbols AC Alternate Current AFCs Alkaline Fuel Cells ASR Area Specific Resistance CCC Ceria Carbonate Composite CDC Calcium Doped Ceria Ce Ceria CO Carbon Monoxide CO2 Carbon Dioxide Cu Copper DC Direct Current DCO Doped Ceria Oxide DSC Differential Scanning Calorimetery EDX Energy Dispersive X-Ray Analysis EIS Electrochemical Impedance Spectroscopy FEI Field Electrons and Ions FRA Frequency Response Analyzer FWHM Full Width Half Maximum GDC gadolinium Doped Ceria H+ Protons HR TEM High Resolution Transmission Electron Microscopy IC Integrated Circuit IKTS Institute for Ceramic Technologies and sintered Materials I-P Current Density versus Power Density ITSOFCs Intermediate Temperature Solid Oxide Fuel Cells I-V Current Density versus Voltage KOH Potassium Hydroxide LMS Strontium Doped Lanthanum Magnate LTSOFCs Low Temperature Solid Oxide Fuel Cells MCFCs Molten Carbonate Fuel Cells NANOCOFC Nano-Composites for Advanced Fuel Cell Technology NASA National Aeronautics and Space Administration NK-CDC Sodium-Potassium Carbonated Calcium Doped Ceria OCV Open Circuit Voltage OH- Hydroxyl Ions PAFCs Phosphoric Acid Fuel Cells PEFCs Polymer Electrolyte Fuel Cells PEMFCs Proton Exchange Membrane Fuel Cells PKR Pakistani Rupee R & D Research and Development rpm round per minute SCCC Solid Carbonate Ceria Composite SDC Samarium Doped Ceria SEK Swedish Krona SEM Scanning Electron Microscopy SOFCs Solid Oxide Fuel Cells SPFCs Solid Polymer Fuel Cells STEM Scanning Transmission Electron Microscopy TEM Transmission Electron Microscopy TGA Thermal Gravimetric Analysis USA United State of America XRD X-Ray Diffraction

Abbreviations and Symbols

XXXV

YDC Yttria Doped Ceria YSZ Yttria Stabilized Zirconia

Symbols $ Dollar A Active Area of the Pellet/Cell Ar Argon Ba Barrium CaO Calcium Oxide Co Cobalt CO3

2- Carbonate Ions d Distance Ea Activation Energy σel Electronic Conductivity σio Ionic Conductivity Fe Feric Gd Gadolinium H2 Hydrogen Hz Hertz K Boltzmann Constant (8.617 X10-5 eV) k kelvin K Potassium kHz kilo-Hertz kW kilowatt L Thickness of the Pellet/Cell La Lanthanum Li Lithium mA/cm2 mili-ampere per square centimeter Mn Manganese MHz mega hertz MW mega watt mW/cm2 mili-watt per square centimeter Na Sodium Ni Nickel O2- Oxygen Ions oC degree centigrade R Resistance of Materials Pt Platinum S/cm Siemens per centimeter Sm Samarium Sr Strontium T Absolute Temperature in Kelvin Y2O3 Yttrium Oxide Zn Zink ZrO2 Zirconium Oxide β Beta λ Lambda ρ Resistivity σ Conductivity Ωcm2 Ohm square centimeter

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