Gas-Crossover and Membrane-Pinhole Effects in Polymer-Electrolyte Fuel Cells

This paper investigates the effects of gas crossover. Specifically, mathematical simulations are conducted to elucidate the fundamental changes in fuel-cell operation as permeation of the various gases through the membrane increases. Two cases are explored, with the first one examining uniform increases in the set of gas-permeation coefficients, and the second one the existence of regions of high gas crossover (i.e., membrane pinholes). For the first case, operation at 120 C is studied and a maximum limit for the hydrogen permeation coefficient of 1 x 10{sup -10} mol/bar-cm-s for a 25 {micro}m membrane is determined. For the second case, it is shown that negative current densities and temperature spikes can arise due to mixed-potential and direct-combustion effects where there are large enough pinholes, thereby impacting performance and water and thermal management.