Three-dimensional simulation of a PEM fuel cell with experimentally measured through-plane gas effective diffusivity considering Knudsen diffusion and the liquid water effect in porous electrodes

Abstract

A fundamental understanding of the gas diffusion properties in porous electrodes, such as catalyst layers (CLs), micro porous layers (MPLs) and gas diffusion layers (GDLs) is necessary for the optimal design of polymer electrolyte membrane (PEM) fuel cell. The conventional Bruggeman correlation has been proven to overestimate through-plane gas effective diffusivity (TP-GED) in GDLs; however, few studies have shed light on the influence of gas diffusion in MPLs and CLs in simulations of PEM fuel cells. In this study, to accurately predict the gas diffusion process and cell performance, a three-dimensional, two-phase and non-isothermal PEM fuel cell model was developed with experimentally measured TP-GED considering Knudsen diffusion and the liquid water effect in porous electrodes. The numerical results indicate that the conventional Bruggeman correlation greatly overpredicts TP-GED in porous electrodes and the oxygen reduction reaction (ORR) within the cathode CL and thus cannot accurately reflect the mass transport loss at high current density. The gas diffusion properties in the cathode porous electrode play a dominant role in determining cell performance. Furthermore, MPLs and CLs exhibit lower TP-GED than GDLs due to Knudsen diffusion; therefore, the distinction among the gas diffusion properties of GDLs, MPLs and CLs must be considered in quantitative modeling and optimization of PEM fuel cells.