Microporous ion-solvating membranes with carboxyl groups for high-performance alkaline water electrolysis

Ion-solvating membranes (ISMs) are broadly used in alkaline water electrolysis (AWE) for their excellent alkaline stability. However, their ionic conductivity often remains a bottleneck. In this work, a series of ISMs featuring hydrophilic microporous structures were developed for AWE. The twisted spirobisindane backbone generated abundant microporosity and carboxyl-induced hydrophilic channels provided ample volume for electrolyte retention, thereby suppressed the swelling ratio. An increased density of carboxyl groups enhanced the hydration environment and promoted the formation of more continuous hydrophilic domains, thereby facilitating ionic transport. The increased incorporation of DMB monomers elevated the hydrophilic of the channels, thereby enhancing ionic conductivity and resulting in the greatest performance of COOH-DMB-40. The COOH-DMB-40 membrane achieved a high alkaline uptake of 78.6% and a low swelling ratio of 19.2% (6 M KOH, 80 °C), yielding a superior ionic conductivity of 134.1 mS cm -1 . In water electrolysis test, COOH-DMB-40 delivered a high current density of 4.4 A cm -2 ( 2.0 V, 80 °C).