Impact of a gas diffusion layer's structural and textural properties on oxygen mass transport resistance in the cathode and performance of proton exchange membrane fuel cells

Abstract

In this work, we used our previously developed method for determination of oxygen mass transport coefficients (k) to evaluate the effects of the gas diffusion layer (GDL) structure and texture on oxygen mass transfer in a cathode electrode and on proton exchange membrane fuel cell (PEMFC) performance. The method is based on measurements of limiting current distributions using oxygen mixtures with different diluents, which allows us to separate a contribution from gas phase molecular diffusion (km) and a combination of Knudsen diffusion and transport through ionomer/water films (kK+film). GDLs with varying microporous layer (MPL) loadings from 50 to 150% were used for the cathode electrode. The lack of an MPL in the GDL resulted in the highest values of km and kK+film but led to poor performance since the MPL plays a critical role in water management. Moreover, the application of a GDL without an MPL allowed the oxygen mass transport coefficient in the catalyst layer (kK+film, CL) to be directly determined. The contribution from the MPL to oxygen transport (kK, MPL) was separated by comparing the results for a cell with a GDL with and without an MPL. An increase in MPL loading caused a gradual decrease in O2 mass transport coefficients and improvement in PEMFC performance in the high power regime. The obtained structure-to-property correlations showed a trade-off in MPL content among mass transport properties, texture and high performance.