Mechanical accelerated stress testing and 4D degradation visualization to evaluate hydrocarbon-based membranes for fuel cell operation at intermediate temperatures

Although fuel cell operation at intermediate temperatures ( e.g. , 100–120 °C) could potentially reduce cost in heavy-duty transportation, the associated durability challenges need systematic investigation. This work employs ex-situ dynamic mechanical analysis and pressure differential accelerated mechanical stress test together with in-situ fuel cell stability and durability tests to evaluate a sulfo-phenylated poly(phenylene)-based composite membrane for intermediate temperature operation. Compared to wet/dry cycling at 80 °C, the membrane shows ∼50 % lower stress of dehydration and 10x slower crack propagation at 110 °C, albeit the risks of creep failure are higher. Fuel cell testing at fixed current density (1.5 A cm −2 ) demonstrates stable performance at 110 °C and 34 % RH for 100 h, with no indication of irreversible degradation over longer durations. However, single-frequency electrochemical impedance spectroscopy shows that RH cycling at such temperatures increases the rate and depth of membrane drying. In-situ RH cycling durability tests combined with electrochemical diagnostics and 4D X-ray computed tomography visualization reveals membrane-electrode incompatibility and localized thinning near the edges as failure modes. Hence, fully hydrocarbon-based designs with proper stress concentration management are believed to enhance the durability of next generation fuel cell membranes at intermediate temperatures. • Operation at 110 °C, low RH reduces membrane dehydration stress and crack growth. • MEAs ran ∼100 h at 110 °C, 34 % RH, 1.5 A cm −2 with no sign of membrane degradation. • RH cycling AST at 110 °C is proposed, guided by stress–strain and hydration data. • Interface incompatibility in CCMs causes membrane failure during 110 °C RH cycling. • RH cycling at 110 °C induces localized creep and membrane thinning near the edges.