Figure shows tmemb plotted against cumulative X-ray dose. The CCMs (prepared with Fumasep® FAA-3-50) in both the lab test (i.e., subjected to electrochemically driven degradation) and the synchrotron-based operando test (i.e., subjected to both electrochemical and X-ray-induced degradation) experienced similar membrane thinning, losing 53 ± 5% and 58 ± 6% of their original thickness respectively, regardless of X-ray exposure. The reference cell, which was exposed to X-rays while minimising electrochemical degradation (by applying only 0.05 A cm⁻² for EIS measurements), displayed a loss of approximately 28% of its original thickness after the same dose as the cell operated at 1 A cm⁻². These findings suggest that membrane thinning is most likely due to chemical degradation rather than X-ray-induced degradation.