The effect of the cathode catalyst layer’s structure and composition on the overall performance of a polymer electrolyte fuel cell (PEMFC) is investigated numerically. The starting point of the sub-grid scale catalyst layer model is the well-known flooded agglomerate concept. The proposed model addresses the effects of Nafion loading, platinum loading, platinum/carbon ratio, agglomerate size and cathode layer thickness. The sub-grid scale model is first validated against experimental data and previously published results, and then embedded within a two-dimensional validated computational fluid dynamics code that can predict the overall performance of the fuel cell. The integrated model is used to explore a wide range of the compositional and structural parameter space, mentioned earlier. In each case, the model is able to correctly predict the trends observed by past experimental studies. The studies show that the presence of an optimal performance with varying Nafion content in the cathode is more due to the local agglomerate-level mass transport and conductivity losses in the polymer coating around the agglomerates than due to the amount of Nafion within the agglomerate. It was also found that platinum mass loading needs to be at a moderate level in order to optimize fuel cell performance. Cathode tortuosity has a significant effect on fuel cell performance at low values of agglomerate radius.

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