Pyridinyl-Based Proton Exchange Membranes With Enhanced Proton Conductivity and Dimensional Stability

The worldwide demand for sustainable energy has accelerated the development of proton exchange membrane fuel cells (PEMFCs) owing to their high efficiency and near-zero emissions. However, the widespread use of perfluorosulfonic acid (PFSA)-based membranes is hindered by high cost, limited thermal stability, and environmental concerns, necessitating the development of fluorine-free alternatives. A key challenge in such systems is overcoming the inherent trade-off between proton conductivity and dimensional stability. Herein, we report the design and synthesis of two series of fluorine-free, pyridinyl-based sulfonated proton exchange membranes, namely polytriazoles (ODPYSH-XX) and poly(sulfone triazole)s (SOPYSH-XX), prepared via Cu-catalyzed click copolymerization with high degrees of sulfonation (DS = 80 and 90). Both membrane series exhibit excellent thermal, mechanical, and dimensional stability. Notably, the sulfone-containing SOPYSH-90 membrane delivers a high proton conductivity of 195 mS cm^{- 1} at 80°C under fully hydrated conditions, along with good oxidative stability (13 h in Fenton's test). These results demonstrate that pyridinyl-based copolymer membranes can effectively balance conductivity and stability, offering a promising pathway toward next-generation proton exchange membranes (PEMs) for PEMFC applications.