Effects of gradient structures of cathode catalyst layers on performance and durability of proton exchange membrane fuel cells

Improving performance and durability of proton exchange membrane fuel cells (PEMFC) is crucial for promoting commercial applications. Deep understanding of the underlying degradation mechanisms is still lacking. In this study, a two-way coupling performance-degradation model is established by incorporating one-dimensional (1D) Platinum (Pt) degradation model into 1D PEMFC performance model, which can predict Pt degradation phenomenon considering Pt dissolution, Pt2+ diffusion and reprecipitation in cathode catalyst layers (CCLs) and resulting performance loss. Effects of gradient CCL structures in terms of ionomer weight, Pt loading and Pt particle size on degradation and performance are investigated. The results show that multi-layer CCLs with more ionomer, more Pt loading, and/or smaller particles near membrane have higher performance, while the opposite gradients present enhanced anti-degradation capacity. Wave-like spatial distributions of Pt mass retention are observed in gradient CCLs, with significant difference across the sub-layer interface. Combined effects of two gradient distributions are also investigated. It is found that for performance, simply add-up roles are followed, namely combining two gradient distributions with higher performance can obtain higher performance, and vice versa. For durability, synergy effects are identified, in which two gradient structures with opposite final Pt mass distribution have competitive influence on Pt2+ local transport, with local Pt2+ diffusion suppressed, the catalyst distribution uniformity improved and performance loss alleviated. The gradient CCL structure considering the balance of performance and durability is identified based on 28 structures studied. Such add-up roles for performance and synergy effects for durability provide new insights for improving the design of PEMFCs.