Pore-scale and multiscale study of effects of Pt degradation on reactive transport processes in proton exchange membrane fuel cells

Understanding catalyst degradation mechanisms and their effects on reactive transport in proton exchange membrane fuel cell (PEMFC) is critical for prolonging cell lifetime. In this study, for the first time pore-scale numerical studies are conducted to explore effects of catalyst degradation on transport and electrochemical reactions in catalyst layers (CLs) of PEMFCs. High-resolution nanoscale structures of pristine and degraded CLs are reconstructed, in which detailed distributions of carbon, Pt, electrolyte and pores are resolved. Different particle size distributions of Pt agglomerates are also considered during the reconstruction. Based on the lattice Boltzmann method, pore-scale models for oxygen diffusion, interfacial dissolution, and electrochemical reaction are developed. Pore-scale modeling is then conducted to evaluate effects of Pt degradation on Pt utilization, active surface area, limiting current density and local transport resistance. It is found that total reaction rate is reduced by approximately 10-30% due to Pt degradation. Such negative effects are more prominent when Pt loading is low or more Pt is distributed in the CL interior, causing 25% and 45% increased transport resistance, respectively. Further, a multi-scale simulation strategy is proposed, and upscaling schemes for integrating pore-scale results into cell-scale models are proposed. The present study demonstrates that pore-scale simulation is a useful tool for understanding coupled mechanisms between Pt degradation and reactive transport phenomena within CLs, and is helpful for providing practical guidance for CL fabrication.