Phenyl vs. Ethyl Spacer-Incorporated Sulfonated Poly(arylene alkylene) Membranes for Proton-Exchange-Membrane Water Electrolysis

Abstract The pursuit of durable and high-performance proton exchange membranes via rational molecular design is crucial for advancing green hydrogen production through water electrolysis. Two series of sulfonated polyaromatic polymers were synthesized via a facile superacid polycondensation followed by postsulfonation, one bearing nonsulfonable ethyl side chains and the other sulfonable phenyl side chains. Morphological characterizations confirmed distinct hydrophilic/hydrophobic phase separation in the ethyl side chain-based sulfonated polyaromatic polymer with an ion exchange capacity of 2.08 mmol g–1. Compared to its phenyl side chain-based counterpart with an ion exchange capacity of 1.99 mmol g–1, the ethyl side chain-based polymer exhibited higher proton conductivity and superior dimensional stability. The membrane electrode assembly based on the polymer with nonsulfonable spacers delivered excellent electrolysis polarization performance and robust durability. The phenyl side chain-based PEM suffered severe edge cracking at the membrane/porous transport layer interface after accelerated stress testing, caused by excessive swelling.