Highly Sulfonated Aromatic Graft Polymer with Very High Proton Conductivity and Low Hydrogen Permeability for Water Electrolysis

An aromatic graft polymer was synthesized for a proton exchange membrane (PEM) by grafting a highly sulfonated poly(phenylene sulfide sulfone) side chain onto a poly(arylene ether sulfone) main chain, thus creating a phase-separated morphology with cocontinuous channels of small hydrophilic ion domains. The graft PEM with the distinct hydrophilic/hydrophobic-separated morphology showed low hydrogen permeability while maintaining high proton conductivity. Along with durable dimensional, mechanical, and thermohydrolytic stabilities, the graft PEM showed effective properties for PEM water electrolysis (PEMWE). The graft PEM afforded a PEMWE performance of 6000 mA cm–2 at 1.9 V, which was 2.1-fold higher than that of N212, and showed a durable performance without loss for 50 h at a high current density (1000 mA cm–2).