Quantitative in-situ analysis of mechanical degradation of the catalyst coated membrane in proton exchange membrane fuel cells: Influences of temperature and relative humidity swing

This work investigates mechanical membrane degradation in fuel cells under variable temperature (50–80 °C) and relative humidity (RH) swing (from 0 % to 60–150 %) using 4D in-situ X-ray computed tomography (XCT) to measure spatiotemporal crack length and area in the catalyst layer and membrane as quantifiable degradation metrics. A scoring system classifies the tests into Tiers 1–3 based on applied hygrothermal stresses correlated to crack data and membrane lifetime. Tier 1 exhibits 2-3x faster crack growth rates and lower membrane lifetime than Tiers 2 and 3, with membrane cracks initiating by 5k RH cycles and propagating rapidly by 15k. In contrast, Tier 3 shows delayed membrane crack onset (after 15k) and slower propagation. The results demonstrate that RH swing wet phase apex is an even stronger driver of stress than temperature. Crack growth rate is validated as a quantifiable in-situ degradation metric, and 4D XCT proves effective for quantifying mechanical membrane degradation. • Dynamic crack dimensions are proposed as an in-situ metric of membrane degradation. • 4D in-situ XCT imaging visualizes and quantifies crack growth over time. • Tiered test scoring links stress severity to crack propagation and lifetime. • Higher wet phase apex and temperature accelerate crack propagation by 2-3x. • Membrane cracks occur by 5k RH cycles for highest stress and 15k for lowest stress.