Chemo-mechanical fracture evolution in reinforced fuel cell membranes revealed by 4D in-situ X-ray computed tomography

The combined chemical and mechanical degradation of a mechanically reinforced fuel cell membrane is investigated through a series of accelerated stress tests under varying temperatures and relative humidity (RH) swings. 4D in-situ X-ray computed tomography is employed to monitor membrane degradation in three spatial dimensions over time, enabling direct observation and quantification of morphological changes. While extensive cathode catalyst layer cracks are present, through-plane membrane failure is primarily driven by anode catalyst layer cracks initiated under flow channels, influenced by both cyclic mechanical and chemical stresses. Quantitative analysis reveals that elevated temperature accelerates membrane crack initiation, increases membrane thinning rates, and significantly reduces operational lifetime. In contrast, the effect of RH swing amplitude on degradation rate is comparatively minor. Relative to pure mechanical degradation, the addition of chemical stresses fundamentally alters the failure mode, promoting earlier onset of anode initiated through-plane cracks and leading to an average 40% reduction in membrane lifetime. These findings underscore the dominant role of temperature driven chemical degradation and highlight the importance of accounting for coupled stress effects in durability assessments of reinforced membranes.