Analysis of Reactant Gas Transport in Catalyst Layers; Effect of Pt-loadings

An analytical in-situ technique was utilized to evaluate reactant gas transport resistance (Rother) in catalyst layers (CLs). It was found that Rother was increased with the decrease of Pt-loadings of the CLs although their thickness was decreased. Effective Knudsen diffusion coefficient was calculated from the pore size distribution and the porosity. It was estimated almost steady regardless of the Pt-loadings. To understand the increase of Rother, a simple transport model was established including Knudsen diffusion resistance in secondary pores and the local transport resistance around the Pt surface. Knudsen diffusion resistance should be decreased in lower Pt-loadings because of the shorter transport length. On the other hand, it was considered that the local transport resistance was increased with decreasing of the effective Pt surface area. Hence, that the effective Pt surface area might be one of the important factors for Rother in the CLs, especially in the lower Pt-loadings.