Atomic Layer Deposition, a rising technique for SOFC and MCFC devices

A.  Meléndez-Ceballos, D. Chery, A. Marizy, V. Albin,

A. Ringuedé, M. Cassir*

* Head Laboratoire d’Electrochimie, Chimie des Interfaces et Modélisation pour l’Energie, LECIME, UMR 7575 CNRS, ENSCP, Paris, France

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High temperature fuel cells & electrolysis

OHOH 222 21

…………+FC

SOEC

ZrO2-Y2O3

Cermet Ni-YSZ

La1-xSrxMnO3

O2- O2-

- → + 2 2

_ 2 2 1

O e O

_ 2 2 2

2 e O H O H + → + -

SOFC: 600-700°C

- e CO O H CO H 2 2 2 2 3 2

+ + → + -

CO32-

- → + + 2 3 2 2 2

2

1 CO - e CO O

Li2CO3- K2CO3

Ni + 2 à 10% Cr ou Al

NiO

MCFC: 600-650°C

↑ lifetime & performance:

Nanostruct./electrochem.

→ half-cells → single cells

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MCFC/SOFC Composite

carbonate/oxide

Nano-scaled layers for SOFC, i.e. CeO2 or ZrO2-based

* Interfacial layers –  Chemical diffusion barrier (cathode/electrolyte interface) –  Electronic barrier (anode/electrolyte interface) –  Catalyst/electrode (at both interfaces) –  Bond layer

* As SOFC electrolytes: µ-SOFC Charge transfer enhancement, resistance ↓ conductivity ↑?

* As corrosion protective layers for interconnects * As active layer at the cathode interface

Cathode (thick or thin)

Electronic barrierElectrolyte (thick or thin)

Anode (thick or thin)

Ionic diffusion barrier

Electrodecatalysts

Interconnect

Interconnect

Protective layer

Protective layer

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Atomic layer Deposition

4

Surface saturation reaction. Thickness: from few nm to µm

R. Puurunen, J. Appl. Phys., 97 (2005) 121301

Gro

wth

spe

ed

Deposition T

ALD window

- Crystaline as deposited

M. Cassir et al., J. Mater. Chem., 20 (2010) 8987

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Litterature orientations

Two main tendencies / use of ALD in SOFCs applications: Ø Low operating temperatures (<500°C) for micro systems such as portable applications. In µ-SOFCs, ultrathin electrolyte layers have a significant role and ALD presents a serious advantage.

ü  The use of ultrathin catalytic or current-collector layers of Pt and Pt grid-patterned catalysts is common.

ü However, this approach supposes the direct use of hydrogen and contradicts the requirements of SOFCs in cogeneration: avoiding precious metals and using fuels as natural gas or biomass which implies a reforming process operating at around 600°C.

Ø  The second tendency concerns electrolyte or catalysts interlayers

and / or cheaper electrode materials activated by ultrathin ALD-processed materials.

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State-of-the-Art Electrolyte, interfaces & current collectors: (i)  Stabilized zirconia (e.g. YSZ): ZrO2, YSZ, ZrO2-In2O3 from few nm to 1 µm. on planar substrates, on porous electrodes and on pre-patterned surfaces (ii)  Ceria and doped ceria (e.g. Gd0.2Ce0.8O2-d = GDC), YDC (iii)   LaGaO3, which is a potential electrolyte when doped: LSGM (La0.9Sr0.1Ga0.8Mg0.2O3) (iv)   BaZrO3, proton-conductor (v)  Pt deposits (catalysts or/and current collectors)

Cathode: a)  LaxSr1-xMnO3 (LSM) b)  La1-xCaxMnO3: potential electrode c)  La1-xSrxFeO3 (LSF)

Anode: LaGaO3-based materials when doped with Sr and Mg

Main teams: Prinz et al., Mc Intyre et al., Bent et al. (Standford), Niinistö et al (Helsinki), Cassir et al. (Paris), Nilsen et al. (Norway), …

Review “Input of Atomic Layer Deposition for Solid Oxide Fuel Cell Applications”, M. Cassir, A. Ringuedé, L. Ninistö, J. Mater. Chem., 20 (2010) 8987

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*  Chao  et  al.,  ACS  Nano,  7  (2013)  2186  **  Fan  et  al.,  Nanole:ers,  11  (2011)  2202.  ***  Fan  et  al.,  J.  Mater.  Chem.,  21,  10903  (2011).  

Ø  Enhancing  O2-­‐  incorpora/on  kine/cs  by  nanoscaled  interlayers**,***  •  17.5  nm  of  YDC  (14.1  mol.  %  Y)  between  YSZ  and  a  porous  Pt  cathode  

enhances  the  performance  of  LT-­‐SOFC  •  ↓  cathode/electrolyte  R  while  increasing  the  exchange  j0  by  a  factor  of  

4  at  300-­‐500  °C  •  Enhancement  of  the  performance  of  the  cell  x  3  

Ø  Enhanced  oxygen  exchange  on  surface-­‐engineered  YSZ*  •  10  nm  of  ALD-­‐processed  YSZ  (14  mol.  %  Y)  on  YSZ  single-­‐crystal  YSZ  ↓  O2  

surface  exchange  coefficient  5  fold  increase  (Isotopic  oxygen  exchange                tests  +  SIMS)  

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 Grain  sizes  of  20-­‐30  nm  result  in  a  high  density  of  grain  boundaries,  which  together  with  the  OH-­‐  incorpora?on  tend  to  provoke  the  proton  conduc?vity  of  the  YSZ  thin  film  (200  nm)  10  mW/cm²  at  450°C  

*  Prinz  et  al.,  Chem.  of  Mater.  21,  3290  (2009)  **  J.  S.  Park  et  al.  ,  Chem.  Of  Mater.,  22,  5366  (2010)  

Ø  Y-­‐doped  BaZrO3  proton  conduc/ng  membranes  (BYZ)  of  100  nm  used  in  a  single  cell  with  Pt  porous  electrodes*  

100  nm  thin  films:  ü ALD-­‐processed:  136  mW/cm²  at  400°C      ü PLD  (pulsed  laser  deposi?on)-­‐  processed  :  120  mW/cm²  at  450°C    

Ø  Proton  conduc/on-­‐based  fuel  cell  with  YSZ  electrolyte  by  ALD**    

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ZrO2-Y2O3 (YSZ) 8 mol% / LSM at 300°C .

990 nm nm 990 nm

990 nm 540 nm 280 nm

-6.5

-6

-5.5

-5

-4.5

-4

-3.5

-315 17 19 21 23 25 27

10000/T(K-1)

Log(σ(S.m-1))

E=0.33eV

E=0.34eV

E=0.40eVж Sample AΔ Sample BÅSample C

100°CT(°C)

200°C300°C

activation energies < 1 eV (bulk YSZ)

σi(280)<σi(540)≈σi(990)

Sl

Rmeas1=σ

C. Brahim, Appl.. Surf. Sci. 253 (2007) 3962 M. Cassir et al. Appl. Surf. Sci., 193 (2002) 120 M. Cassir et al., Patent WO02053798 (2002)

-4.00E+02

-2.00E+02

0.00E+00

2.00E+02

4.00E+02

6.00E+02

0.00E+00 2.00E+02 4.00E+02 6.00E+02 8.00E+02 1.00E+03 1.20E+03 1.40E+03

Z'/Ohm

-Z''/Ohm 6

54

3

210 -1

-2

6

54

3210

-1

-2

65 4 3

ж Sample AΔ Sample BÅ Sample C

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Alternative electrolyte, yttria-doped ceria YDC (10/20 mol%)

400 nm, 6 mol% / ss

342 nm, 7 mol% / La0.8Sr0.2FeO3

300°C

342 nm, 7 mol% / La0.8Sr0.2FeO3

0.E+00

2.E+05

4.E+05

6.E+05

8.E+05

1.E+06

0.E+00 2.E+05 4.E+05 6.E+05 8.E+05 1.E+06 1.E+06 1.E+06Z' (Ohms)

Z" (O

hms)

0.05V0.1V0.15V0.2V0.25V

3

4

5

YDC

laye

r

Electrode reaction

-7

-6

-5

-4

-3

-2

-1

010 15 20 25 30

(10000/T) / K -1

log (s

igma /

S.m

-1)

YSZ 20at% [7,10]

YDC 16at%

400°C 300°C500°C 200°C-7

-6

-5

-4

-3

-2

-1

010 15 20 25 30

(10000/T) / K -1

log (s

igma /

S.m

-1)

YSZ 20at% [7,10]

YDC 16at%

400°C 300°C500°C 200°C

-  T > 420°C, σYDC > σYSZ - εr 10 x lower / bulk YDC: thin layer better dielectric material

E. Ballée et al., Chem. Mater., 2009, 21, 4614-4619 EFC 2013 Rome

•  In3+ size close to Zr4+ –  r(In3+)=0.80 A° –  r(Zr4+)=0.84 A°

Ø Ionic & electronic conductivity = f(In3+ ratio)

ZrO2-In2O3 system

••Ο

ΧΟ ++→ VOInOIn Zr

ZrO

32 '2

32

2

-4

-3.5

-3

-2.5

-2

-1.5

-1

-0.5

00% 20% 40% 60% 80% 100%

In mol%

log σ

(S/c

m)

Ionic conductivity Electronic conductivity

-4

-3.5

-3

-2.5

-2

-1.5

-1

-0.5

00% 20% 40% 60% 80% 100%

In mol%

log σ

(S/c

m)

Ionic conductivity Electronic conductivity

A. Ringuedé, P. Mourot, C. Alvarez Lugano, J-C. Badot and M. Cassir, J. New Mat. for Electrochem. Syst. 9 (2006) 201-208

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30 40 50 60 70 802θ (°)

Inte

nsité

(u.a

)

¿

¿

¿ ¿

Þ

Þ

Þ

Þ

Þ

¿ZrO2 ÞLSM

(a)

(b)

(111

)

(200

)

(220

)

(311

)

Þ

IDZ ionic conductor

320 nm of IDZ (34 mol%) /LSM 480 nm of IDZ (26 mol% ) / LSM 380 nm of IDZ (22 mol%) / NiO-YSZ Well-covering, dense and uniform cubic-structured deposits

λKαCo= 1.78897 Å

(a)  320 nm IDZ; 34 mol% (b)  480 nm IDZ; 26 mol%

•  Deposition at 300 °C

⇒  no annealing treatment

2 µm 1 µm 1 µm 2 µm

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Gradient Gradient 1 µm 1 µm

1,06 µm

ZrO2-In2O3 (gradient) / YSZ

Epaisseur désirée (nm)

Composition en InO1,5 désirée (mol%)

200 90 200 60 200 45 500 25

YSZ

IDZ

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Electrical behaviour of the gradient

7

8

9

10

11

12

13

14

15

11 12 13 14 15 16 17 18 19 20 21

10000/T /K-1

Log

((R

/e)/(Ω

/m))

YSZ30%50%65%90%gradient HT

300°C400°C500°C

% In ≤ 65 % ⇒ R with % In

65%

50% 30%

90%

% In = 90 % ⇒ R

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Theoretical/experimental approach of CeO2-based catalysts at the SOFC (or MCFC) anode

(Ph.D of T. Désaunay, sept. 2012) Ø  Oxygen source at SOFC anode: enhancement of hydrogen oxidation /

would allow the direct oxidation of CH4 without carbon deposit Ø  State of the surface: fundamental role / reactivity

Ø  Understanding mechanisms at the molecular level: higher performance

Ø  Theoretical approach of the behaviour of ceria and its interface reactivity by DFT

Ø  Nanoparticles of CeO2 synthesised by hydrothermal route Ø 

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Ø  Reactivity: T-programmed reduction (TPR): T order: nanocubes (100) < nanowires (110) < nanooctahedra (111)

> > Ea (kJ/mol) : 70 < 130 < 430

Ø  Thin-layered CeO2 / NiO-YSZ by ALD

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Al2O3 (102)

Y:ZrO2 (100)

SrTiO3 (100)

Non oriented

Thin layers for MCFC by ALD

H2 + CO2 + H2O ↓

Anode"Ni + 3% Cr"Li2CO3-Na2CO3/LiAlO2

Ni2+ → Ni (short-circuit)

LixNi1-xO → ↑"Cathode "O2 + CO2 ↑

!

Ni + 3% Cr"

Li2CO3-Na2CO3/LiAlO2

Thin layer < 1 µm"Ni/NiO

Protection of MCFC separator plates

Protection of the cathode cathode

Current collector Anticorrosion layer MCrAlY bond layer

Stainless steel

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Coatings

CeO2 TiO2 Nb2O5 Co3O4

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TiO2 + 2Li+ +CO32− → Li2TiO3 +CO2

LixTiyNiO3.59 ± 0.06 (x ≤ 0.5 and y ≤ 0.36): crystal structure similar to NiO

TiO2 coating (300 nm) / Ni in molten Li2CO3-K2CO3 at 650°C Before After 230 h Mapping: well-distributed mixed phase Ti-Ni-O

Sol. /

wt.ppm

Ni TiO2 / Ni (50 nm)

TiO2 / Ni (150 nm)

TiO2 /Ni (300 nm)

Ni 15 8.2 6.5 10

Ti 1.3 1.2 < 1

OCP evolution vs. time in Li2CO3-K2CO3 at 650OC, 230 h. a) Ni, b) TiO2 (50 nm), c) CeO2 (27 nm), d) Co3O4 (50 nm)

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Sample  Ni Porous   TiO2

50 nm  CeO2

20 nm  Co3O4 50 nm  

Measured Value

(wt. ppm)  15   8   10   12  

Conclusions Ø  ALD deposits

–  Crystalline at low T without annealing –  Dense, conformal –  Good composition and thickness control –  Production of thin layers with composition gradient –  Speed growth relatively low (15 nm/h IDZ)

Ø  Pellets ≠ µ or nano-structured thin layers Ø  Modification of the electrochemical properties with composition gradient Ø  Correlation between nanostructures and electrochemical properties?

- More active area (surface kinetics enhanced) - Reduced interfacial electrode-electrolyte reactions

- Thermal constraints control (rapid ageing of the fuel cell materials) Ø  Modelling effort required for complex materials surface organization Ø  Use of thin layers in new high-temperature electrochemical devices

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