Tailoring cationic functional groups for enhanced stability and performance in Polysulfone-based anion exchange membranes

Anion exchange membranes (AEMs) are promising materials for electrochemical systems due to their compatibility with alkaline environments, enabling cost-effective use of non-precious metal catalysts. However, alkaline stability of cationic functional groups remains a key challenge. In this study, polysulfone-based AEMs were synthesized with two ammonium functional groups: trimethylammonium (TMA) and triethylammonium (TEA). NMR spectroscopy (including Pulsed Field Gradient method and relaxometry) and electrochemical impedance spectroscopy were employed to assess microstructure, conductivity, and durability. The shorter TMA chain enhanced hydrophilicity, conductivity, and alkaline stability. Fuel cell tests confirmed the poor chemical stability of qPSU-TEA, which degraded rapidly under operating conditions. In contrast, qPSU-TMA outperformed a commercial membrane (FAA-3–50) under identical conditions, achieving a peak power density of 220 mW/cm² at 60 °C and maintaining high performance at 80 °C. These findings highlight the robust electrochemical stability and interface integrity of qPSU-TMA at elevated temperatures, and underscore the critical role of cationic group design in optimizing AEM performance and durability.