Lattice Boltzmann study of the effect of catalyst layer structure on oxygen reduction reaction within a PEMFC

Abstract

The catalyst layer (CL) structure has a great impact on proton exchange membrane fuel cell (PEMFC) performance. In this study, the microporous structure of a cathode CL is reconstructed via a stochastic algorithm. Subsequently, the lattice Boltzmann method (LBM) is used to investigate the influence of the CL structure regarding carbon carrier and platinum (Pt) particle sizes and ionomer thickness on oxygen reduction reaction (ORR) processes within the cathode CL. The LBM simulation results indicate that an increased carbon carrier size promotes oxygen transport through the CL pores owing to the decreased tortuosity of the porous CL but reduces the overall ORR rate. A larger Pt particle size leads to a reduction in the number of reaction sites but shortens the ionomer thickness for oxygen diffusion to the reaction sites. The oxygen transport resistance through the ionomer increases with increasing ionomer thickness and thus degrades the overall ORR rate. However, an excessively small ionomer thickness leads to the exposure and shedding of Pt, thereby reducing the number of reaction sites. The findings here demonstrate that proper design of the carbon carrier and Pt particle sizes and ionomer thickness are essential for achieving a CL with high oxygen transport performance and overall ORR rate.