Sulfonated Poly(Phenylene sulfone) blend membranes finding their way into proton exchange membrane fuel cells

We demonstrate performance and durability of a fluorine-free poly(phenylene-sulfone) membrane for proton exchange membrane fuel cells. Sulfonated poly(phenylene-sulfone) (EW 220 g·eq−1; sPPS-220) has been prepared and processed by acid/base blending with 25 wt% poly(benzimidazole) (sPPS-220/PBI-O). A blend membrane with a nominal EW 463 g·eq−1(ion exchange capacity of 2.16 meq·g−1) has been fabricated by solution co-casting on a commercial production line. Blend component fractions are chosen to meet Nafion 211's specific conductivity and obtain mechanical robustness. Blend membrane has significantly lower gas permeability than Nafion under both dry (RH = 30%) and wet (RH = 95%) conditions, significantly higher storage modulus and no softening at high temperature. Like pure-sPPS, blend membrane is hydrolytically stable up to T = 180 °C in water. Single-cell H2/air fuel cell tests demonstrate higher open-circuit voltage and similar performance under load conditions compared to Nafion. Still, high mass transport polarization is likely due to water condensation at the cathode side. This increases membrane swelling and thus electroosmotic water drag reducing hydration at the anode side and leading to flooding of the cathode. Under accelerated stress conditions at low relative humidity, sPPS-220/PBI-O is more durable than Nafion. Possible explanations are i) lower gas crossover reduced radical formation rate and ii) high intrinsic stability of sPPS.