In-Plane Nonuniform Degradation in Proton Exchange Membrane Fuel Cells during 3000 h of Operation

During operation, proton exchange membrane fuel cell (PEMFC) stacks experience nonuniform in-plane degradation due to the uneven distribution and synergistic coupling of multiple physical fields, including mass transport, thermal, electrical, and mechanical effects. This nonuniformity leads to the formation of localized accelerated degradation regions, which significantly deteriorate cell performance. To date, most related studies have focused on performance degradation at the single-cell level or on the overall degradation behavior of stacks, while systematic investigations into the in-plane nonuniform degradation behavior of engineering-scale stacks under long-term dynamic operating conditions, as well as their cross-scale evolution mechanisms, remain limited. In this study, the degradation behavior of a 100 kW PEMFC stack consisting of 354 cells was systematically investigated. By comparatively screening and disassembling the most severely degraded single cell (Cell #7), and combining electrochemical measurements with multiscale physical characterization techniques, the localized degradation mechanisms were elucidated. The results indicate that excessive assembly pressure and structural mismatch between the frame and sealing gasket induce significant stress concentration at the cell edges, leading to an approximately 5-fold increase in hydrogen crossover. The cathode gas diffusion layer exhibits structural degradation, including reduced hydrophobicity, carbon fiber loosening, and PTFE loss. Meanwhile, the corrosion current density of the bipolar plate increases by a factor of 2–3, accompanied by pronounced electrochemical corrosion and the emergence of distinct ″boundary line″ features. In parallel, coupled thermal–mechanical–chemical effects accelerate ionomer degradation, carbon support corrosion, and Pt agglomeration within the catalyst layer, resulting in a significant reduction in electrochemical surface area. These synergistic degradation mechanisms render the edge region the most vulnerable zone for in-plane nonuniform degradation. This study elucidates the cross-scale degradation pathways of PEMFCs and provides important insights into their in-plane nonuniform degradation mechanisms under long-term dynamic loading conditions.