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T.Maiyalagan and Prof. B. Viswanathan

Department of Chemistry, Indian Institute of Technology, Madras

Chennai 600 036, India

Nitrogen containing carbon nanotubes as Nitrogen containing carbon nanotubes as supports for Pt – alternate anodes forsupports for Pt – alternate anodes for

Fuel cell applications.Fuel cell applications.

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Thermal Energy Mechanical Energy

Chemical Energy Electrical Energy

FUEL CELLSFUEL CELLS

Fuel Cell

ICE

Direct Energy Conversion Vs Indirect Technology

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• Batteries– Needs recharging– Dangerous chemicals

• Internal combustion engines - Carnot limitations - Moving parts and hence friction - Noisy

C. K. Dyer, J. Power. Sources, 106 (2002) 245

BATTERIES/ICE /FUEL CELLSBATTERIES/ICE /FUEL CELLS

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EFFICIENCY

RELIABILITY

CLEANLINESS

UNIQUE OPERATING CHARACTERISTICS

PLANNING FLEXIBILITY

FUTURE DEVELOPMENT POTENTIAL

FUEL CELLS – ADVANTAGESFUEL CELLS – ADVANTAGES

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VARIOUS TYPES OF FUEL CELLSVARIOUS TYPES OF FUEL CELLS

dadf

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2H2 + O2 2H2O

2H2 4H+ + 4e-

O2 + 4H+ + 4e-

2H20

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HOW DOES PEMFC WORK HOW DOES PEMFC WORK ??

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Electrolyte frame Bipolar plate

Anode catalystCathode catalyst

O2

H2

Stack of several hundred

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ADVANTAGES OF ADVANTAGES OF LIQUIDLIQUID FUELS FUELS

• Higher volumetric and gravimetric densities

• Easier to transport

• Storage and handling

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CHEMICAL AND CHEMICAL AND ELECTROCHEMICALELECTROCHEMICAL DATA DATA ON VARIOUS FUELSON VARIOUS FUELS

FUEL G0, kcal/mol

E0theor (V) E0

max (V) Energy density (kWh/kg)

Hydrogen -56.69 1.23 1.15 32.67

Methanol -166.80 1.21 0.98 6.13

Ammonia -80.80 1.17 0.62 5.52

Hydrazine -143.90 1.56 1.28 5.22

Formaldehyde -124.70 1.35 1.15 4.82

Carbon monoxide

-61.60 1.33 1.22 2.04

Formic acid -68-20 1.48 1.14 1.72

Methane -195.50 1.06 0.58 -

Propane -503.20 1.08 0.65 -

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High specific energy density

Clean liquid fuel

Larger availability at low cost

Easy to handle and distribute

Made from Natural gas and renewable sources

Possible direct methanol operation fuel cell

Economically viable option

WHY WHY METHANOLMETHANOL ??

Heinzel et al, J. Power Sources 105 (2002) 250

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Direct Methanol Fuel Cell (DMFC)

CH3OH + H2O CO2 + 6H+ + 6e-Eo = 0.046 V(electro-oxidation of methanol)

Driven LoadAnode Cathode

Methanol + Water

Carbon Dioxide

Anode Diffusion Media

Anode Catalyst Layer

e- e-

H+

H+

H+

Oxygen

Water

Acidic ElectrolyteSolid Polymer Electrolyte: PEM (Proton Exchange Membrane)

Cathode Catalyst Layer

Cathode Diffusion Media

3/2O2 + 6H+ + 6e- 3H2OEo = 1.23 V

Overall Reaction

CH3OH + 3/2O2 +H2O CO2 + 3H2O Ecell = 1.18 V

Acidic electrolytes are usually more advantageous to aid CO2 rejection since insoluble carbonates form in alkaline electrolytes

Nafion 117

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Advantages of DMFC Technology• Longer membrane lifetime due to operating in

aqueous environment• Reactant humidification is not requiredCompared to H2 Systems with Methanol Reformer• Low operating temperature of DMFC results in low

thermal signature• DMFC system has faster start-up and load following• DMFC system is simpler and has lower weight and volume• Can use existing infrastructure for gasoline

G.G. Park et al., Int.J. Hydrogen Energy 28 (2003) 645

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Status of DMFC Technology• Large number of companies working on

DMFC technology for consumer applications

• Commercialization of DMFCs for cell phones and laptops expected within 2-3 years

• Cost of DMFCs is coming down, and becoming competitive with Li batteries

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DIFFICULTIES IN DMFCDIFFICULTIES IN DMFC

POOR ANODE KINETICS

FUEL CROSSOVER

ELECTROCATALYSTS

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Challenges for DMFC Commercialization

COST Cost of stacks DECREASE OF NOBLE METAL LOADINGS

Utilization Stability

Template synthesised CNT as the support for Pt, Pt-Ru, Pt-MoO3

Present objectivePresent objective

Overall objective:Overall objective:

Reduce catalyst cost for direct methanol fuel cellsReduce catalyst cost for direct methanol fuel cells

CNT: Concentric shells of graphite rolled into a cylinder

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High Temperature

Why Supported Catalyst?

What is the support?How to choose betterSupport ?

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THE PROMISE OF NANOTUBES SUPPORTTHE PROMISE OF NANOTUBES SUPPORT

● Single walled nanotubes are only a few nanometers in diameter and up to a millimeter long.

● High conductivity.

● High accessible surface area.

● High dispersion.

● Better stability.

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Why Nitrogen containing carbon nanotubes?Why Nitrogen containing carbon nanotubes?

Good electronic conductivity.

Electronic structure and band gap can be tuned by varying the nitrogen content .

Addition of nitrogen increases the conductivity of the material by raising the Fermi level towards the conduction band .

Catalytic properties of the surface are determined by the position of the Fermi level of the catalyst. Consequently Fermi level acts as a regulator of the catalytic activity of the catalyst.

The nitrogen functionality in the carbon nanotube support determines the the size of Pt by bonding with lone pairs of electrons at the nitrogen site.

Pt bound strongly to nitrogen sites so sintering doesn’t takes place.The increased electron donation from nitrogen bound carbon nanotubes to Pt might be responsible for enhancement in kinetics of methanol oxidation.

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PVPN=12.9%

PPYN=21.2%

PVIN=33.0%

PPP N= 0%

Present workPresent work

Synthesis Of Nitrogen containing carbon nanotubes

NITROGEN CONTAINING POLYMERS

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impregnation

Polymer solutionALUMINA MEMBRANE

carbonization

48 % HF 24 HRS

CNT

Schematic DiagramSchematic Diagram

Polymer

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SYNTHESIS OF PVP-CNTSYNTHESIS OF PVP-CNT

Carbonization Ar atm

48% HF 24 hrs

PVP InDCM

PVP/alumina

Alumina membrane

CNTPVP

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Carbonization apparatusCarbonization apparatus

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Thermogravimetric analysisThermogravimetric analysis

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ELEMENTAL ANALYSISELEMENTAL ANALYSISCALCULATED EXPERIMENTAL at 9000C

SAMPLE % C % N % H % C % N % H

PPP-CNT 93.0 0.00 4.9 92.3 0.00 1.8

PVP-CNT 64.82 12.62 8.17 86.98 6.63 0.81

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SEM PICTURE OF PVP -CNTSEM PICTURE OF PVP -CNT

(a) The top view of the CNTs.

27(b) The lateral view of the well aligned CNTs ( Low magnification) .

SEM PICTURE OF PVP -CNTSEM PICTURE OF PVP -CNT

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SEM PICTURE OF PVP -CNTSEM PICTURE OF PVP -CNT

(c) The lateral view of the well aligned CNTs ( High magnification) .

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HR-TEM images of carbon nanaotubes obtained by the carbonisation of polyvinyl pyrolidone (a-b) Carbonisation at 1173 K, 4hrs

TEM PICTURES OF PVP -CNTTEM PICTURES OF PVP -CNT

200nm

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RAMAN SPECTRUMRAMAN SPECTRUM

G -Band

D-Band

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FT – IR SPECTRUMFT – IR SPECTRUM

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FT – IR SPECTRUMFT – IR SPECTRUM

C=N

C=CC-NO-H

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275 280 285 290 295

284.5

287.05

C1s

Inte

nsi

ty (

arb

.un

its)

Binding Energy (eV)

392 396 400 404

397.6 399.4

N1s

Inte

nsi

ty (

arb

.un

its)

Binding Energy (eV)

XPS - SPECTRAXPS - SPECTRA

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Loading of catalyst inside nanotubes

73mM H2PtCl6

12 hrs

H2 823 K3 hrs

48% HF 24 hrs

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TEM PICTURE OF Pt/CNTTEM PICTURE OF Pt/CNT

EDX spectrum

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TEM PICTURE OF Pt/CNTTEM PICTURE OF Pt/CNT

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Electrode FabricationElectrode Fabrication

  Ultrasonicated, 30 min

Dispersion (10 l) / Glassy Carbon (0.07 cm2)

  Dried in air

 

5 l Nafion (binder)

Solvent evaporated

ELECTRODE

10 mg CNT/ 100 l water

ELECTROCHEMICAL STUDIESELECTROCHEMICAL STUDIES

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METHANOL OXIDATIONMETHANOL OXIDATION

Cyclic Voltammograms of (a) Pt in 1 M H2SO4/1 MCH3OH run at 50 mV/s

39Cyclic Voltammograms of (b) GC/ETek 20 % Pt/C Nafion in 1 M H2SO4/1 MCH3OH run at 50 mV/s

40Cyclic Voltammograms of (c)GC/CNTpvp-Pt--Nafion in 1 M H2SO4/1 MCH3OH run at 50 mV/s

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Electrochemical activity of the electrodes based on carbon nanotubes in comparison with commercial catalysts for methanol oxidation

Electrode Activity

Ipa(mA/cm2)

Pt 0.076

GC/CNT-Pt-Naf

GC/ETek20%Pt/C-Naf 11.4

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Data evaluated from cyclic voltammogram run in 1M H2SO4/1M CH3OH at 50 mV/s

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ConclusionsConclusions

1. The template aided synthesis of carbon nanotubes using polymer as a carbon source yielded well aligned carbon nanotube with the pore diameter matching with the template used.

2. The higher electrochemical surface area of the CNT and the highly dispersed catalytic particles may be responsible for the better utilization of the catalytic particles. The tubular morphology might be the reason for the better dispersion.

3. The higher activity of the nitrogen containing carbon nanotube catalyst suggest that the Nitrogen present in the carbon nanotube (after carbonisation) plays an important role not only in the dispersion, but also in increasing the hydrophilic nature of the catalyst.

4. There is a correlation between the catalytic activity of the carbon nanotube electrode material and the nitrogen concentration (at%). Future work will be focused on ways to enrich the N content on the surface of CNT supports.

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