Molecular Engineering of Phosphine Oxide-Enriched Sulfonated Polytriazoles for Fluorine-Free Proton Exchange Membranes

Abstract The development of fluorine-free proton exchange membranes (PEMs) is crucial for reducing the environmental concerns associated with perfluorinated membrane materials. Herein, we report a series of sulfonated polytriazoles (SPTs; TABPSH-XX) via simple “click” copolymerization, wherein phosphine oxide (P═O) units are strategically integrated into both hydrophilic and hydrophobic sections of the copolymer framework. The development of high-molar-mass copolymers is confirmed by viscosity and SEC analyses. Their chemical architectures are confirmed by the NMR (1H, 13C, and 31P), XPS, and EDX analyses. The TABPSH-XX copolymers exhibit ion exchange capacities ranging from 1.84 to 2.27 mequiv/g. Morphological studies reveal well-developed, interconnected, hydrophilic–hydrophobic phase-separated microstructures with defined interfaces, facilitating efficient proton transport. The incorporation of high proportions of P═O functionalities promotes strong ionic and acid–base interactions, resulting in membranes with excellent thermal, mechanical, and dimensional stability. Among the series, the TABPSH-90 membrane exhibits the highest proton conductivity (121 mS/cm) at 90 °C under fully hydrated conditions and demonstrates enhanced oxidative stability (≥6.5 h). These findings demonstrate an effective molecular design strategy for developing high-performance fluorine-free sulfonated PEMs and highlight the potential of P═O-enriched SPTs for next-generation membrane-based electrochemical applications.