Modeling the Influence of GDL and flow-field plate parameters on the reaction distribution in the PEMFC cathode catalyst layer

In this paper, a two-dimensional cross-the-channel model was applied to investigate the influence of gas diffusion layer (GDL) property and flow-field geometry on the local reaction rate in the PEMFC cathode catalyst layer. The model predictions show that the rate of consumption of oxygen or current density under the land area may differ considerably from that under the channel. Simulation results indicate that for a fixed channel width, increasing the channel-to-land width ratio results in improved water transport and positively impacts the overall reaction rates at high overpotential. However, too high ratio may retard electron transport and thus lead to worse cathode performance. Numerical simulation results revealed that GDL electrical conductivity and thickness have a strong influence on how the chemical species and electrons are transported to the active catalyst sites. Depending on the electrical conductivity of GDL, the region of higher reaction rate may occur either under the land or under the channel. Consideration of orthotropic electrical conductivity of GDL affects the simulation results significantly highlighting the need to improve our understanding of GDL transport coefficients. Simulation of GDL compression effects showed that the total current density is not affected significantly but current density distribution is. The extent of reactant bypass through the GDL from one channel to the other depends on the GDL permeability and results in a significant enhancement in reaction rates.