Gas permeability of catalyzed electrodes in polymer electrolyte membrane fuel cells

Abstract

For polymer electrolyte membrane (PEM) fuel cells, the importance of mass transport property, gas permeability, in gas diffusion layer (GDL) is widely recognized with less attention being paid to catalyzed electrode (GDL with a catalyst layer). In this study, the contribution of the catalyst layer to the overall gas permeability of the electrode is experimentally investigated for different catalysts with a range of Pt loadings at various temperatures for air, oxygen and nitrogen gases. Results indicate that the gas permeability of the GDLs can be reduced by 58–77% with the presence of a catalyst layer. For the constant Pt loadings, the electrodes with higher Pt/C ratios (e.g., 60% Pt/C) show larger gas permeability than those with lower ratios (e.g., 30% Pt/C) due to their smaller thicknesses and higher porosity. Similarly, for the electrodes with the same type of catalysts, the gas permeability is higher for lower Pt loadings. Further, the effective gas permeability of the catalyst layers alone is about two orders of magnitude smaller than that of the GDLs. Additionally, operating at higher temperatures slightly enhances the permeability. Oxygen gas has a higher permeability than air and nitrogen, but the differences are small. These results highlight the importance of catalyst layer, hence the Pt loadings and Pt/C ratios, in determining the mass transport throughout the entire electrode in PEM fuel cells.