FUEL CELL SYSTEMS

S. Basu New Delhi Department of Chemical Engineering Indian Institute of Technology Delhi INDIA e- Load Water 1. Fuel chamber 2. Oxidant chamber 1 4 2 3. Anode (Pt) 4. Electrolyte Fuel 3 5 Oxidant 5. Cathode (Pt/C) (H ) 2 O2/Air + - H2 2 H +2e (Anode) + - 2 H +1/2 O2 +2e H2O (Cathode)

H2 + 1/2 O2 H2O (Overall)

9 Automobile 9 Efficient Power Generation 9 Distributed Power Gen. 9 Environmental Friendly 9 Portable Electronics Eqpt. Fuel Cell Families

Phosphoric Acid Cathode Anode o H+ 220 C

Solid Polymer Cathode Anode o o H+ 30 C- 80 C

Alkaline Air Cathode - Anode Fuel 50 oC- 200 oC OH

Molten Carbonates o Cathode = Anode 650 C CO3

Solid Oxides Cathode Anode o o O= 700 C – 1000 C Alkaline Fuel Cell ALKALINE FUEL CELL

Alkaline electrolyte - - Anode H2 + 2OH Æ 2H2O + 2e

- - Cathode 1/2O2 + H2O + 2e Æ 2OH

Overall H2 + 1/2O2 Æ H2O + electrical Energy +heat

Poisoning: - 2- CO2 +2OH (CO3) + H2O ¾ Depletion of KOH ¾ Poisoning of cathode surface with carbonates Myth !

9Kordesch, K. et al., (1999), Intermittent Use of a Low-Cost Alkaline Fuel Cell-hybrid System for Electric Vehicles, J. Power Sources, Vol. 80, pp.

9McLean, G. F. et al. (2002) An assessment of alkaline fuel cell technology, Int. J. Hydrogen Energy 27 507

9Gülzow, E., and Schulze, M. (2003), Long-Term Operation of AFC Electrodes With CO2- Containing Gases, J. Power Sources, Polymer Electrolyte Membrane Fuel Cell (PEMFC)

Hydrogen Fuel Cell Direct Alcohol Fuel Cell (DAFC)

Fuel Processor Fuel Cleaning System Fuel Pure H2 Electricity Fuel Cell Direct Methanol Fuel Cell Direct Ethanol Fuel Cell (DMFC) (DEFC) ™ Reduce CO adsorption on Pt at High Temp ™ Higher power density at high temperature ™ Easy breakage C-C bond in DEFC at High Temp. Problems at high temperature operation- • Poor proton conduction at High temperature • Nafion membrane should remain hydrated for proton conduction e- Load

Water 1. Fuel chamber 2. Oxidant chamber 1 2 3. Anode (Pt) 4 4. Polymer Electrolyte Membrane Fuel 3 5 Oxidant (PEM) (H ) 5. Cathode (Pt/C) 2 O2/Air + - H2 2 H +2e (Anode) + - 2 H +1/2 O2 +2e H2O (Cathode)

H2 + 1/2 O2 H2O (Overall) DIRECT METHANOL FUEL CELL (DMFC)

Load

Air/H O CH3OH/H2O/CO2 Catalyst Layers 2 ANODE CATHODE

PEM e- e- H+

H2O

CH3OH

Current collector + Reactant Distributor Current collector + Reactant Distributor Air CH3OH/H2O Diffusion Layers Reaction Mechanism

Anode Reactions (Oxidation of Methanol) :

+ - CH3OH + Pt Pt - CH2OH + H + 1e (1) + - Pt-CH2OH + Pt Pt - CHOH + H + 1e (2) Pt-CHOH + Pt Pt-CHO + H+ + 1e- (3) Pt - CHO + Pt Pt - C≡O + H+ + 1e- (4a) or Pt Pt-CHO + Pt C=O + H+ + 1e- (4b) Pt Water dissociation

+ - Pt + H2O Pt-OH + H + 1e (5)

+ - Pt-OH + Pt-CO 2Pt + CO2 + H + 1e (6) Cathode Reactions (Reduction of Oxygen) :

O2 + Pt Pt -O2 (7)

+ - Pt-O2 + H + 1e Pt -HO2 (8)

Pt-HO2 + Pt Pt - OH + Pt -O (9)

+ - Pt -OH + Pt -O + 3H +3e 2 Pt + 2 H2O (10) Overall Reaction :

CH3OH + 3/2 O2 CO2 +2H2O (11) Perfluro-sulphonic acid Membrane

Hydrophilic part

Hydrophobic part International Status • Published literatures are very few - 1. Doyle, M., Choi, S., Proulx, G., High-Temperature Proton Conducting Membranes Based on Perfluorinated Ionomer Membrane-Ionic Liquid Composites, J. Electrochem. Soc. 147 (2000), 34-37 2. Arico, A.S., Creti, P., Antonucci, P.L., Antonucci, V., (1998). Comparison of ethanol and methanol oxidation in a liquid-feed solid polymer electrolyte fuel cell at high temperature. Electrochemical and solid state letters, 1, 66-68. • Research work is going on – R & D Labs, Univ. (US, Canada, UK, Japan) National Status • Work on PEMFC/DMFC – IISc, SPIC, NCL, CECRI, IIT M • No work on membrane for high temperature operation • No work on DEFC - Some preliminary work by SPIC Science Foundation Electrode

• Anode: Pt/Ru (40 % / 20%) /C Pt - 2 mg/cm2 0.4 mg/cm2 • Cathode: Pt/C (20%) Pt – 2mg/cm2 similar Polymer Electrolyte Membrane (PEM) • Perfluoro Sulphonic Membrane (Nafion DE 5112) PEM MEA 40 oC – 80 oC Anode PTFE

Carbon cloth

Cathode Bipolar plate

Schematic of DEFC

Load

Air/H O C2H5OH/H2O/CO2 Catalyst Layers 2

ANODE CATHODE

PEM e- e- H+

H2O

Current collect or + Reactant Distri butor

Current collector + Reactant Distributor C2H5OH/H2O Diffusion Layers Air

Anode: (catalyst : Pt / Ru / C ) - + C2H5OH + 3 H2O 12 e + 12 H + 2 CO2 Cathode: (catalyst : Pt / C ) - + 3 O2 + 12 e + 12 H 6 H2O Overall:

C2H5OH + 3 O2 3 H2O + 2 CO2 Why Ethanol ?

• Higher theoretical moles of H2 per moles (or litre) of fuel • Renewable resources • Lower toxicity, vapour pressure and flash point • Less corrosive Reaction Path Process Parameters Input 1. Temp : 145o – 150o C 2. Feed: anode - 1M EtOH Soln at 80 oC o cathode – O2 /Air humidified at 80 C 3. Catalyst loading : 2 mg/cm2 reduce loading 4. Anode / Cathode : 4 atm 5. Cross-sectional Area: 9 cm2

Output (single cell, expected) • Voltage (open circuit): 0.8 V • 0.5 V at 60-120 mA/cm2 • 30 – 60 mW/cm2 Solid Oxide Fuel Cell (SOFC)

2e- 2e- Porous Porous Cathode Anode Reaction Products + Heat

O-2 ion (H2O, CO2, H2, CO etc.)

O Air 2 H2 (and other fuels: CO, CH4 ...)

Cathode Reaction: Anode Reactions: + - H 2H + 2e 1/2 O + 2e- O-2 Catalyst Thin Solid 2 2 ion Interfaces Electrolyte 2H + +O-2 H2O ion SOFC = High temperature (700 to 1000oC) solid state fuel cell with ceramic, oxygen ion conducting electrolyte Tubular SOFC Materials and Processing

Component Material Fabrication Process

Air Electrode Doped LaMnO3 Extrusion-Sintered Electrolyte ZrO2(Y2O3) Electrochemical Vapor Deposition Interconnection Doped LaCrO3 Plasma Spraying Fuel Electrode Ni-ZrO2 (Y2O3) Slurry Coat-Electrochemical Vapor Deposition

Operating around 950-1000°C

Courtesy of Siemens- Westinghouse, Pittsburgh, PA Tubular Geometry Solid Oxide Fuel Cell

Interconnection

Electrolyte

Air Fuel Electrode Flow

Air Flow Fuel Electrode Tubular SOFC Small Stack of Tubular SOFC

24 SOFCs, each tube with 2.2 cm diameter and 150 cm long. Planar Solid Oxide Fuel Cells

„ Operating temperature ~ 700-750 ºC

„ Use numerous fuels

„ Efficiently produce power at varying loads The SOFC Stack

„ Cells are sealed via a high temperature compressive gasket Delphi SOFC APU - Gen 1 to Gen 2

SOFC APU System Evolution

Generation 1 Generation 2 SOFC APU SOFC APU

Gen 1 Stacks Provided by Global Thermoelectric 155 Liters 60.5 Liters 12/2002 204 kg 12/2000 75 kg Delphi – Battelle Generation 2 Stack Cell and Stack Development Scale Up

106 cm2 Active Area

34 cm2 Active Area

34 cm2

3.5 cm2

Button-Cell Intermediate-Scale Full-Scale Small active area Full active area Primarily for repeating unit for repeating unit for cathode, stack –for design stack –for design electrolyte and performance and performance and anode optimization and optimization and materials development development development Delphi – Battelle Generation 2 Stack Development Summary

‹ Multiple sintered cells (12 cm x 12 cm) have been successfully fabricated. ‹ Research and development is being done in collaboration with Battelle. ‹ Process development being done internally at Delphi.

‹ Multiple stacks from 1-cell to 30-cell have been fabricated. Two 15- cell ISMs (Integrated stack module) have also been fabricated and have been tested in the APU systems.

Integrated stack module-ISM Cassette with cell (repeating unit) 30-cell stack under test (Two 15-cell stacks+ current collector + load frame) FUTURE DIRECTION!

SOFC Poisoning PEMFC Cost DAFC High Temperature MeOH cross over AFC Poisoning

Karl Kordesch Zevco Company

Zevco AFC Module (2000) 6000 hours 100 mA/cm2

Michael, P. D. ‘An Assessment of the prospect for fuel cell-powered cars ETSU, UK (2000) Most Advanced Fuel Cells

„ Many fuels:

„ Gaseous: H2, hydrocarbons, natural gas, biogas, coal gas „ Liquid: alcohol, gasoline, diesel „ Solid: gasified coal and biomass „ Many applications: „ Stationary and mobile „ Target: universal system? Comparisons

¾ Performance Current Den.(at 0.7V) Power at 0.7 V Pressure Temp mA/cm2 w/cm2 psig oC

AFC 450 0.315 atm H2-air 75 115 0.081 same 40 PEMFC 250 0.175 same 60 125 0.088 same 70

¾ Cost Astris (LC200-16) 240 W AFC 2400 USD H-Power (PowerPEM-PS250) 250 W PEMFC 5700 USD DAIS-Analytic (DAC-200) 200 W PEMFC 8500 USD

Kordesch, K., et al.’Revival of AFC hybrid system for electric vehicles’ Proc. Fuel Cell Sem., Palm Springs 1998 Solid Oxide Fuel Cells - SOFCs

„ Why: SOFCs Employ Solid State Electrolyte, hence: Corrosion Reduced; Water Management Eliminated; Very Thin Layers/Cell Components Possible; Fuel Flexibility High; Internal Reforming and Combined Heat/Power Cycles Possible, etc….

„ Problems: High Temperature (850-1000oC) Related, e.g., Longer Time Required for Start-up, Expensive Materials Involved, Durability/ Robustness/Cost Issues, etc…

„ Reduced Temperature SOFCs: Dropping the Operating Temperature to Below 700oC ─ called Intermediate Temperature SOFCs. Eliminates high temperature problems Reformer Complexity - SOFC vs PEM

Autothermal / Steam Reformer Solid Oxide Partial Oxidation Fuel Cell Reformer Stack > 900 °C 800 °C 700-1000 °C

High Temperature SOFC Shift Reactor SOFC reformer and stack run at similar temperatures and can be closely coupled.

Low Temperature Shift Reactor Preferential PEM Oxidation (CO clean-up) PEM reformer + stack run at very different temperatures. PEM A complex, multi-stage reformer system must be Fuel cell stack carefully thermally managed at each step. 80 °C Courtesy of Delphi Corp., Rochester, NY MULTI-FUEL ALKALINE FUEL CELL

„ Fuels: MeOH, EtOH, NaBH4 „ Cathode: MnOx /Carbon paper „ Anode: Pt-black/Carbon paper/Ni

1 Fuel and electrolyte mixture 2 Exhausted fuel and electrolyte 3 Peristaltic pump for input 4 Peristaltic pump for output 5 Load 6 Anode terminal 7 Cathode terminal 8 Air 9 Anode electrode 10 Cathode electrode 11 Fuel and electrolyte mixture 12 Magnetic stirrer 13 Anode shield Comparative performance of alkaline fuel cell

OCV: Open circuit voltage; SCCD: Short circuit current density

Reference Fuel Anode Cathode Electrolyte Operating OCV SCCD Temp. (V) (mA/ cm2)

Verma, Methanol Fe (III)- Graphite 6 N KOH 25o C 0.85 18 2000 treated treated with Ag (I)

Verma, Methanol Al (II)- Graphite 6 N KOH 25o C 1.4 54 2000 treated treated with Ag (I)

Amendol Sodium Au/Pt Johnson Anion 25o C 1.1 152 a et al., borohydrie (97:3) Matthey conducting 1999 membrane

Li et al., Sodium Zr-Ni Pt- Black Na+ form of 60o C 1.2 300 in press borohydrie alloy (1 mg/cm2) Nafion 117 Fuel Cell Lab at IIT Delhi Alkaline fuel cell

Direct alcohol fuel cell ANODE PREPARATION

Nafion + C-Powder Ultrasonic mixing for 30 min at 25 oC Nafion-C-Slurry + Pt-Powder Ultrasonic mixing for 30 min at 25 oC Catalyzed Slurry Spread on C- Paper Catalyzed C-Paper Dried in Oven for 30 min at 80 oC

Catalyzed C-Paper + Nickel Mesh Hydraulic press:100 kg/cm2, 120 oC For 5 min.

Anode Sintering, 300 oC for 2 hr Size: 3x3 cm2

Cathode Preparation : MnOx / C / Ni – Similar manner CHEMISTRY OF ALKALINE FUEL CELL (AFC)

™ Reaction at cathode - - 4e + O2 + 2H2O Æ 4 OH

‰ Reaction at anode „ Methanol - - CH3OH + 2OH Æ HCHO + 2H2O + 2e - HCHO + 2OH Æ HCOOH + H2O + 2e - - HCOOH + 2OH Æ CO2 + 2H2O + 2e „ Ethanol

- - C2H5OH + 2OH ÆCH3CHO + 2H2O + 2 e

„ NaBH4 - - i. NaBH4 + 8 OH Æ NaBO2 + 6H2O + 8 e ii. NaBH4 + 2H2O Æ NaBO2 + 4H2 pH < 7 or High Temp Cyclic Voltammetry

1.40E-02 Nitrogen satutared Air saturated

) 1.00E-02 -2 cm A

m 6.00E-03 y ( t i

dens 2.00E-03 ent r r u

C -2.00E-03

-6.00E-03 -0.9 -0.7 -0.5 -0.3 -0.1 0.1 Voltage (V)

Cyclic voltammetric curves of the cathode (3 mg cm-2 manganese oxide) in 3 M KOH solution saturated with air and nitrogen gas. Scan rate 5 mVs-1 Polarization curve for different fuels in AFC at 25 oC

Anode loading Pt-black : 0.4 mg/cm2;Fuel: 1 M conc. 1.4

1.2 Methanol Ethanol Sodium borohydride 1.0

0.8 Voltage (V)

0.6

0.4 0 1020304050 Current density (mA/cm2) Power density versus current density for different fuels in AFC at 25 oC

35

) 30 2 Methanol 25 Ethanol Sodium borohydride 20

15

10

Power density (mW/cm 5

0 0 1020304050 Current density (mA/cm2) Polarization curve for different fuels in AFC at 60 oC

1.4

1.2 Methanol Ethanol 1.0 Sodium Borohydride

0.8 Voltage (V)

0.6

0.4 0 1020304050 Current Density (mA/cm2) Power density versus current density for different fuels in AFC at 60 oC

35 Methanol

) 30

2 Ethanol Sodium borohydride 25

20

15

10

Power density (mW/cm 5

0 0 1020304050 Current density (mA/cm2) Comparison of cell performance for different fuel at different temperatures

OCV: Open circuit voltage; SCCD: Short circuit current density; MPD: Maximum power density

25o C temperature 60o C temperature

Fuel OCV(V) SCCD MPD OCV (V) SCCD MPD (mA/cm2) (mW/cm2) (mA/cm2) (mW/cm2)

MeOH 0.93 22.00 13.86 1.15 45.0 31.50

EtOH 1.00 20.75 11.42 1.19 30.0 18.00

NaBH4 1.20 30.00 16.50 1.36 35.3 24.14 Polarization curves (3 M KOH, 1 M methanol) for alkaline fuel cell on different loadings of manganese oxide as a cathode catalyst

1.2 10 1 mg cm-2 3 mg cm-2 )

1.0 8 -2 5 mg cm-2 )

V 0.8 6 ( y (mW cm t age 0.6 4 Volt

0.4 2 Power densi

0.2 0 0 5 10 15 20 25 30 Current density (mA cm-2)

Anode loading: 0.2 mg/cm2 Polarization curves (3 M KOH, 1 M ethanol) for alkaline fuel cell on different loadings of manganese oxide as a cathode catalyst

1.2 16 1 mg cm-2 -2 14 3 mg cm

1.0 )

-2 -2 5 mg cm 12 0.8 ) 10

0.6 8

Voltage (V 6 0.4 4

0.2 Power density (mW cm 2

0.0 0 0 10203040 Current density (mA cm-2) Polarization curves (3 M KOH, 1 M sodium borohydride) for alkaline fuel cell on different loadings of manganese oxide as a cathode catalyst

1.2 20

1.0 ) -2 1 mg cm-2 15 3 mg cm-2 W cm 0.8 5 mg cm-2 10 ltage (V)

o 0.6 V

5 0.4 Power density (m

0.2 0 0 1020304050 Current density (mA cm-2) Performance Data for a Thin Film Electrolyte - SOFC

Direct oxidation for hydrocarbon fuels (methane):

2- - CH4 + 4O CO2 + 2H2O + 8e

Fuel: CH4 Oxidant: air Fuel flow: 50 cm3 STP/min Anode: Ni-YSZ-YDC Electrolyte: bi-layered thin films, YSZ, 2 µm

YDC, 15(Y2O3):85(CeO2) 0.5 µm Cathode:

YSZ:LSM, La0.8Sr0.2MnO3 E. P. Murray et al. Nature, 400 (2000) 648 Performance Data for a Thin Film Electrolyte -SOFC

Direct oxidation, hydrocarbon fuels (n-butane):

2- - C4H10 + 4O 4CO2 + 5H2O + 26e

Fuel: H2, C4H10 Oxidant: air Fuel flow: Anode: Cu-ceria composite H , 800°C Electrolyte: YSZ, 60 µm 2 Cathode: 700°C YSZ:LSM, La Sr MnO 700°C 0.8 0.2 3 800°C C4H10 S. Park et al. Nature, 404 (2000) 265 Performance Data for Alcohol (600°C)

400 1.0 )

300 -2

0.8 m ) Wc V ( 200 m ( e Methanol g

0.6 y t a i t l ns

Vo 100 0.4 Ethanol r de e w 0.2 0 o P

0 500 1000 -2 CurrentCure edensitynt density (mAcm(mAcm ) -2)

0.3 - 0.5 mm thick electrolyte Operating Temperature Effects

32 2400 2100 24 1800 1500 T= 700 C 16 1200 T= 800 C T= 700 C T= 600 C 900 T= 800 C Stack Power (W) Stack Voltage (V) 8 600 T= 600 C 300 0 0 0 50 100 150 200 0 40 80 120 160 200 Stack Current (A) Stack Current (A) Fuel Composition Effects

Comparison of Predicted SOFC Performance

Flow rate, Net usable Thermal Combined Fuels kg/s heat for co- power efficiency, generation, efficiency, % kW % Bio-fuel 10-4 0.4 18 64 Hydrogen 2.26×10-5 0.8 30 78 Reversible system, electrical work done = Gibbs free energy released, H2 + ½ O2 Æ H2O

E = - gf / 2F = 1.48 V (for hydrogen)

Cell eff = VC (actual) / 1.48

Eff. η = µf VC (actual) / 1.48

Fuel utilization coeff. µf Nernst Eq. 1/ 2 R T ⎛ aH . a O2 ⎞ E = E + ln⎜ 12 ⎟ o 2 F ⎜ a ⎟ ⎝ H 2O ⎠ Conclusions

™Fuel Cell – PEMFC, AFC, SOFC

™Multi fuel alkaline fuel cell is feasible

™ Use: Automobile, Stationary Application

™ Cost - reduction

Acknowledgment: MNES for funding the project Thank you !