Impacts of channel/land width ratio on the durability of sulfo-phenylated poly(phenylene)-based fuel cell membranes

This work investigates the effects of flow field channel/land width (C/L) ratio on the durability of sulfo-phenylated poly (phenylene) (sPPP) hydrocarbon-based membranes under chemo-mechanical accelerated stress tests (CM-ASTs). Miniaturized fuel cells with C/L ratios of 4.0, 1.75, and 0.625 are evaluated, supported by electrochemical diagnostics, in-situ single-frequency electrochemical impedance spectroscopy, X-ray computed tomography visualization, and finite element modeling (FEM) to understand degradation mechanisms. At high C/L ratio of 4.0, localized membrane creep under the land limits the longevity of sPPP membranes to 25-50 h. Reducing the C/L ratio to 1.75 and 0.625 extends durability to 310-330 and beyond 600 h, respectively, with the latter cell showing no failure within the test duration. FEM simulations show that lower C/L ratios produce a more uniform stress distribution and reduce the predicted in-plane tensile stresses during RH cycling. Experimentally, lower C/L ratios result in lower membrane dehydration during the prolonged dry phase, mitigating dehydration-stress-driven degradation. A reinforced PFSA membrane tested at C/L ratio of 4.0 exhibits minimal degradation after 600 h due to its lower swelling and sensitivity to hydration changes, and better plate-electrode–membrane compatibility. The insights gained herein highlight the importance of flow field design for advancing next-generation fluorine-free fuel cell membranes.