Effects of cathode gas diffusion layer design on polymer electrolyte membrane fuel cell water management and performance

The effects of a microporous layer (MPL) on performance and water management of polymer electrolyte fuel cells are investigated. The presence of an MPL on the cathode side is found to slightly improve performance, although the voltage gain is less significant than that obtained by wetter reactants. The effect of the MPL on water management depends on the cathode inlet-gas humidity. Differences in water crossover rate are insignificant for wet cathode feed (RH = 75%), while they are significant for dry feed (RH = 25%). A model based on transport resistance of the MPL is proposed to explain the experimental trends observed. Modeling results suggest that the presence of the MPL on the cathode side causes a reduction of the water flux from the cathode catalyst layer to the flow channels, effectively promoting water back diffusion through the membrane. Higher cathode humidity reduces the driving force for water transport from the electrode to the gas channels, also reducing the importance of the water transport resistance due to the presence of the MPL.