Advanced Proton Conducting Membranes Enabled by Amine‐Crosslinked Sulfonated Poly(Arylene Ether) Networks for High Efficiency in Proton Exchange Membrane Fuel Cells

ABSTRACT The widespread adoption of fuel cell technologies depends heavily on the development of proton exchange membranes (PEMs) with high proton conductivity and excellent dimensional and chemical stability. In this study, a series of sulfonated polyaromatic PEMs based on S4FP4 are synthesized by crosslinking with varying concentrations (0.1%–1%) of 1‐(4‐Aminophenyl)‐2,3‐dihydro‐1,3,3‐trimethyl‐1H‐inden‐5‐amine (PIDA). Our findings show that incorporating low to moderate PIDA concentrations (0.1%–0.3%) yields S4FP4‐PIDA0.1 and S4FP4‐PIDA0.3 membranes that exhibit exceptional proton conductivities, surpassing Nafion 211 by 61% and 48%, respectively, while also demonstrating improved dimensional and oxidative stability. Single‐cell efficiency analysis confirms the superior output of these membranes, achieving peak power densities of 1.25 W/cm 2 and 1.17 W/cm 2 , respectively, both outperforming Nafion 211 (1.14 W/cm 2 ). Hydration properties indicate that, despite a decrease in overall water uptake with increased crosslinking, the membranes exhibit stronger water–ion interactions and more efficient localized hydration around ionic sites. Conversely, membranes with higher PIDA content (0.5%–1%) exhibit reduced proton conductivity and lower fuel cell performance, despite their high durability. These findings highlight the importance of carefully designing the membrane structure to achieve a balanced interplay between proton conductivity and the polymer network's dimensional and oxidative stability.