Performance and durability of PEM fuel cells operated at sub-freezing temperatures
- Los Alamos National Laboratory
The durability of polymer electrolyte membrane (PEM) fuel cells operated at sub-freezing temperatures has received increasing attention in recent years. The Department of Energy's PEM fuel cell stack technical targets for the year 2010 include unassisted start-up from -40 {sup o}C and startup from -20 {sup o}C ambient in as low as 30 seconds with < 5 MJ energy consumption. Moreover, the sub-freezing operations should not have any impact on acieving other technical targets including 5000 hours durability. The effect of MEA preparation on the performance of single-PEM fuel cells operated at sub-freezing temperatures is presented. The cell performance and durability are dependent on the MEA and are probably influenced by the porosity of the catalyst layers. When a cell is operated isothermally at -10 {sup o}C in constant current mode, the voltage gradually decreases over time and eventually drops to zero. AC impedance analysis indicated that the rate of voltage loss is initially due to an increase in the charge transfer resistance and is gradual. After a period, the rate of decay accelerates rapidly due to mass transport limitations at the catalyst and/or gas diffusion layers. The high frequency resistance also increases over time during the isothermal operation at sub-freezing temperatures and was a function of the initial membrane water content. LANL prepared MEAs showed very little loss in the catalyst surface area with multiple sub-freezing operations, whereas the commercial MEAs exhibited significant loss in cathode surface area with the anode being unaffected. These results indicate that catalyst layer ice formation is influenced strongly by the MEA and is responsible for the long-term degradation of fuel cells operated at sub-freezing temperatures. This ice formation was monitored using neutron radiography and was found to be concentrated near cell edges at the flow field turns. The water distribution also indicated that ice may be forming mainly in the GDLs at -10 {sup o}C and could be concentrated in the catalyst layer at -20 {sup o}C.
- Research Organization:
- Los Alamos National Laboratory (LANL), Los Alamos, NM (United States)
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- AC52-06NA25396
- OSTI ID:
- 960496
- Report Number(s):
- LA-UR-08-05052; LA-UR-08-5052; TRN: US201006%%1162
- Resource Relation:
- Journal Volume: 16; Journal Issue: 2; Conference: PRIME 2008 ; October 12, 2008 ; Honolulu
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
ANODES
AUGMENTATION
CATALYSTS
CATHODES
DIFFUSION
ELECTRIC POTENTIAL
ELECTROLYTES
ENERGY CONSUMPTION
FREEZING
FUEL CELLS
ICE
IMPEDANCE
LANL
LAYERS
MASS
MEMBRANES
NEUTRON RADIOGRAPHY
OPERATION
PERFORMANCE
POLYMERS
POROSITY
PROTON EXCHANGE MEMBRANE FUEL CELLS
STACKS
START-UP
SURFACE AREA
TRANSPORT
WATER SUPPLY