Alkaline stable cross-linked anion exchange membrane based on steric hindrance effect and microphase-separated structure for water electrolyzer

This study focuses on the development of cross-linked anion exchange membranes (AEMs) based on polystyrene-b-poly(ethylene-co-butylene)-b-polystyrene (SEBS), known for its ether free backbone and excellent chemical stability. The cross-linked SEBS (X-SEBS-BC) membranes were synthesized using an eco-friendly method with SnCl<inf>4</inf> under mild conditions. A cross-linking agent, 1,4-diazabicyclo[2.2.2]octane; (DABCO), was employed to enhance ion conducting channels and improve alkaline stability by preventing degradation. The resulting membranes exhibited low swelling, high conductivity, and significant chemical stability in alkaline environments. This is achieved through the rigid cage-like structure of DABCO, which hinders syn-periplanar conformational changes and protects against the degradation of S<inf>N</inf>² and ylide reactions. Their well-defined microphase-separated morphology, observed through TEM, supports effective ion transport. Notably, the X-SEBS-BC-0.81 membrane showed excellent alkaline stability, with minimal degradation in 3 M KOH over 30 days at 30 °C and 3.3 % degradation in 1 M KOH over 600 h at 50 °C. In water electrolysis tests, this membrane demonstrated superior performance (0.95 Acm⁻² at 2.0 V), surpassing the commercial FAA-3-50 membrane by 82 %. These findings highlight the potential of X-SEBS-BC membranes for advanced AEM applications, particularly in water electrolysis.