Effects of catalyst loading gradient in catalyst layers on performance of polymer electrolyte membrane fuel cells

In this paper, numerical and analytical approaches are presented to evaluate the effect of catalyst loading gradient in the catalyst layer (CL) of a polymer electrolyte membrane (PEM) fuel cell. The model is developed based on agglomerate catalyst and accounts for reactant spices and charge (ion and electron) transport in the cathode side of a PEM fuel cell. The special variation of catalyst loading is considered in two direction, "across the layer" from membrane/CL interface to gas diffusion layer (GDL) and "in catalyst plane" under the channels and land areas in the channel direction. A fuel cell test stand is designed and built to facilitate experimental validation of the model. The primary basic analytical investigation shows improvement in fuel cell performance in comparison with uniform catalyst loading. More detailed numerical simulations confirm the analytical results and indicate that the catalyst loading distribution in the both directions has the significant effect on the catalyst utilization. It is also found that the key question of where to apply more catalyst to increases power density is addressed by the concept of locations at which the reaction occurs at the highest rate.