Publication Detail
The Design, Construction and Testing of an Electrically Segmented PEM Fuel Cell
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UCD-ITS-RR-95-20 Research Report |
Suggested Citation:
Prabhu, Manohar K. (1995) The Design, Construction and Testing of an Electrically Segmented PEM Fuel Cell. Institute of Transportation Studies, University of California, Davis, Research Report UCD-ITS-RR-95-20
The current distribution across the cross-section of a single cell in a proton exchange membrane (PEM) fuel cell system is known to vary. This variation is due to deviations in the power generation capability of each portion of the reactive area. This phenomenon was hypothesized to be caused by temperature gradients and reactant and product concentration fluctuations along the distance of the reactant gas flow channels. The magnitude of this performance variability and the influence of reactant pressure, temperature and oxidant stoichiometric ratio on current distribution were investigated, utilizing a specially designed and constructed solid polymer electrolyte cell (Nafion®-117) fueled with compressed hydrogen and air.
This paper describes the design, construction and testing of the segmented fuel cell project, in which the reaction area of the test fuel cell was separated into five electrically independent sections, each of which was monitored for levels of temperature and voltage and current produced. Each of the segments corresponded to a different distance along the hydrogen and air gas flow channels, with all five segments in series along the gas flow channels. Testing conditions were variable from segment and gas temperatures of 40°C to 85°C, reactant pressures from 1 bar to 3 bar and bulk stoichiometric ratios of air supplied from 1 to greater than 5. Construction of the project equipment required particular attention to the low heat capacities of the gases involved and the need to saturate the gas streams with non-condensing water vapor.
Results indicated the need for adequate heat transport from the reaction area to stabilize temperatures. Current drawn from each segment greatly affected its temperature. Additionally, high lateral thermal conductivity was observed, implying that most heat transfer in fuel cells employing graphite current collectors occurs via conduction through the current collectors, rather than via convection through the reactant gas streams.
Additional results illustrated the need for precise temperature and humidity control on the incoming gas streams and on the graphite current collectors. Proper control was shown to maximize performance characteristics primarily by enhancing water management. As expected, the partial pressures of reactants were also influential in determining segment performance.
This paper describes the design, construction and testing of the segmented fuel cell project, in which the reaction area of the test fuel cell was separated into five electrically independent sections, each of which was monitored for levels of temperature and voltage and current produced. Each of the segments corresponded to a different distance along the hydrogen and air gas flow channels, with all five segments in series along the gas flow channels. Testing conditions were variable from segment and gas temperatures of 40°C to 85°C, reactant pressures from 1 bar to 3 bar and bulk stoichiometric ratios of air supplied from 1 to greater than 5. Construction of the project equipment required particular attention to the low heat capacities of the gases involved and the need to saturate the gas streams with non-condensing water vapor.
Results indicated the need for adequate heat transport from the reaction area to stabilize temperatures. Current drawn from each segment greatly affected its temperature. Additionally, high lateral thermal conductivity was observed, implying that most heat transfer in fuel cells employing graphite current collectors occurs via conduction through the current collectors, rather than via convection through the reactant gas streams.
Additional results illustrated the need for precise temperature and humidity control on the incoming gas streams and on the graphite current collectors. Proper control was shown to maximize performance characteristics primarily by enhancing water management. As expected, the partial pressures of reactants were also influential in determining segment performance.
Master's Thesis.