Side-Chain Sulfur-Enhanced Hydrogen-Bonding Networks in Sulfonated Poly(arylene alkane)s for High Proton Conductivity

Sulfonated poly(arylene alkane)s with all-carbon aromatic backbones are promising proton exchange membrane (PEM) materials, but their high conductivity generally relies on a high degree of sulfonation, which often causes excessive water swelling and compromises dimensional stability. Here, we report a side-chain design that introduces sulfur-containing hydrogen-bonding sites to promote proton transport while preserving dimensional stability. Haloalkyl-functionalized poly(arylene alkane)s were grafted with mercaptoalkyl sulfonates, yielding sulfonic acid-terminated side chains bridged by thioether linkages. The resulting polymers form continuous ionic domains through backbone/side-chain microphase separation, while thioether and sulfonic acid groups cooperate to construct dense hydrogen-bonding networks for proton hopping. The optimized SPBT-1 membrane exhibits a high proton conductivity of 308 mS cm–1 at 80 °C, 1.6 times that of NR212, with comparable swelling. The H2/air fuel cell based on SPBT-1 achieves a high power density of 780 mW cm–2 and stable open-circuit operation over 80 h. These results demonstrate side-chain sulfur functionalization as an effective strategy for highly conductive PEMs.