Non-uniform degradation mechanisms of PEMFCs under dynamic load conditions of high temperature and low humidity

Proton exchange membrane fuel cells (PEMFCs) face durability challenges under dynamic load and high-temperature, low-humidity (HTLH) conditions. While in-plane non-uniform degradation in large-area fuel cells (LAFCs) is acknowledged, the spatiotemporal degradation patterns remain not fully understood. This study investigates a 291 cm 2 PEMFC during a 200-h HTLH dynamic load cycling test. Utilizing periodic electrochemical diagnostics and microstructural characterizations, it is revealed that performance degradation is a non-linear, spatially-dependent process. The cell operates under a continuous slow degradation state (e.g., 0–120 h and 180–200 h), primarily governed by the cathode inlet and anode inlet/outlet regions. In these areas, progressive mechanical defects and severe ionomer redistribution significantly elevate concentration polarization. Concurrently, the cell faces a risk of sudden rapid degradation (manifesting as loading failure). It is strongly associated with abrupt mechanical damage (cracking and delamination) specifically at the cathode outlet region, once accumulated humidity cycling stresses reach a critical threshold. To mitigate this risk, an in-situ recovery strategy based on high-current operation is proposed. The water produced under high-current conditions promotes ionomer hydration and swelling. This process partially fills mechanical defects and helps the cell return to the baseline slow-degradation state. Furthermore, ECSA loss is attributed to coupled catalyst layer degradation, involving Pt oxidation/dissolution-related processes, limited Pt coarsening, ionomer redistribution, and reduced electrochemical accessibility of Pt sites. This study highlights that spatial degradation severity is governed by sealing constraints and the local water state, providing a theoretical foundation for optimizing heavy-duty LAFCs under HTLH operating conditions.