An improved two-dimensional agglomerate cathode model to study the influence of catalyst layer structural parameters

A two-dimensional model for PEM fuel cell cathode has been developed. The model treats the catalyst layer as agglomerates of polymer electrolyte coated catalyst particles. In this improved model, transport of the two charged species - electrons and ions - as well as that of the chemical species within the catalyst layer is considered. In addition, the transport of electrons through the gas diffusion layer is also considered. The model prediction shows that the cathode overpotential inside the catalyst layer is non-unifonn influenced by the channel-land geometry, which implies that the implicit constant overpotential assumption in the commonly employed ultra-thin catalyst layer model is not an accurate representation of actual situation and may lead to overprediction of current densities. Unlike a majority of the multidimensional models that predict the current density to be higher either under the flow-channel area or under the land region, our model illustrates that the location of higher current (electrode reaction rate) changes from the region under the flow channel to that under the land area depending on the overpotential. Our simulation results suggest that charge transport, both electron conduction and the proton migration, is as important as oxygen diffusion in determining the overall electrode reaction rate. Using reaction effectiveness factor analysis, we found that catalyst utilization within the agglomerate is extremely poor at high current densities. The two-dimensional model was employed to investigate the effects of catalyst layer structural parameters including Nafion and platinum loadings and distributions on the cathode performance. The model predicts that there is an optimum level of Nation loading. (c) 2004 Elsevier Ltd. All rights reserved.