Deciphering degradation in porous transport layer-based hydrogen‑oxygen PEMFCs: Insights from 6600-cycle operando durability tests

The long-term durability of porous transport layer (PTL)-based hydrogen–oxygen proton exchange membrane fuel cells (HO-PEMFCs) remains poorly understood to their practical deployment in enclosed environments. To address this gap, a comprehensive 6600-cycle operando accelerated durability test was conducted under dynamic load conditions simulating real operational profiles. Degradation behavior was systematically investigated through the integration of multiple in-situ electrochemical diagnostics, operando water visualization with a transparent cell, and post-test morphological/compositional characterization, enabling quantitative analysis of membrane thinning, catalyst layer thickness variations, and localized structural changes. The results systematically reveal three key degradation mechanisms in the CCM: severe membrane thinning exceeding 40% occurred near the cathode inlet, accompanied by macroscopic fracture, resulting from synergistic chemical and mechanical degradation. Additionally, the cathode catalyst layer (CL) experienced localized thinning from approximately 8.2 μm to 4 μm under the rib region due to swelling, shedding, and gas starvation. Pronounced crack propagation was also observed in the channel region of the CL, primarily induced by PTL-exacerbated wet-dry cycling. These degradation mechanisms were further amplified by the use of a thicker proton exchange membrane coupled with thinner carbon paper, imposing enhanced cyclic stress on the catalyst layer. This work provides critical experimental insights for optimizing the structural design and assembly processes of PTL-based HO-PEMFCs.