Performance and durability of fluorine-free sulfonated polymer proton exchange membranes: A comparative study on backbone architecture

Developing high-performance, stable, non-fluorinated sulfonated hydrocarbon polymers as proton exchange membranes (PEMs) to replace conventional perfluorosulfonic acid (PFSA) materials has attracted significant research interest. Importantly, the long-term chemical durability of fuel cells remains a more critical challenge than achieving high peak cell performance. This study systematically evaluates the structure-performance-stability relationships of five representative sulfonated aromatic polymers featuring comparable ion exchange capacities (IECs). Key membrane properties, including water uptake, proton conductivity, mechanical properties, and oxidative stability, were comprehensively characterized. Among the candidate materials, sulfonated poly(oxindole terphenylene) (SPOTP-100)—which incorporates a rigid backbone paired with side-chain sulfonic acid groups—exhibited superior oxidative stability during Fenton's tests. Furthermore, SPOTP-100 demonstrated exceptional fuel cell durability, exceeding 560 h at 80 °C and 100% relative humidity (RH) under a current density of 0.30 A cm −2 , significantly outperforming the reference polymers (<200 h). These results underscore the decisive role of polymer architecture in dictating PEM lifetime and offer strategic design pathways for durable, high-performance non-fluorinated membranes.