Parametric analysis of a solid polymer fuel cell using current distribution mapping
During operation of the solid polymer fuel cell (SPFC). its performance is limited by the concentrations of hydrogen and oxygen at the reaction interfaces and in most SPFC designs, the hydration state of the membrane. Since in general, the concentrations of water and the gaseous species vary along the flow channel, the performance is also likely to change along the flow channel. In order to study this phenomenon, a measurement system was developed to map the current distribution across the electrode surface. The current distribution has been measured by dividing one of the current collectors into a number of electrically isolated segments. The current flowing through each of the segments was measured while maintaining a constant potential across the surface of the gas diffusion layer. Two separate segmented current collectors were developed. The first was used to measure the current distribution for an 80 cm2 single cell, and the second was used to investigate the local current densities around a single flow channel. The effects of the feed gas humidities on the spatial current density in the 80 cm2 fuel cell were investigated for two different membrane-electrode configurations. With Nafion 117 as electrolyte and at a cell temperature of 80°C. the membrane was found to dehydrate in the initial portion of the gas flow channel when the relative humidity of both the hydrogen and oxygen feed gases was less than 50%. With a Gore-Select membrane electrode assembly (hydrogen and air. temperature- 60°C). the membrane was sufficiently hydrated at all feed gas humidification conditions. The performance of the cell was found to deteriorate at higher feed gas humidities as a result of the lower partial pressures of the reactant gases. Measurements of the effects of gas pressures, stoichiometries and humidities on the length-wise and width-wise perfonnance around a single flow channel (Gore-Select membrane electrode assembly) are discussed in relation to a gas flow model.