Highly Efficient and Durable Water Electrolysis at High KOH Concentration Enabled by Cationic Group‐Free Ion Solvating Membranes in Free‐standing Gel Form

Abstract The degradation of fixed cationic groups in most anion exchange membranes (AEMs) under alkaline environments limits their durability for alkaline water electrolysis (AWE). Ion‐solvating membranes (ISMs) have emerged as a promising alternative to address this issue. Herein, a cationic group‐free ion solvating membrane in a free‐standing gel form (ISM‐PBI‐FG) is presented, created through a sol‐to‐gel transformation process followed by KOH imbibing. This approach yields a 3D porous microstructure composed of entangled polybenzimidazole (PBI) nanofibrils, achieving 89% porosity, which enables ultrahigh alkali uptake (346% in 6 M KOH) and exceptional ionic conductivity (763 mS cm −1 at 80 °C). The absence of cationic groups avoids the attack by OH − , thus ensures good alkaline stability with a conductivity retention rate of 91.6% over a 3120 h ex situ test in 6 M KOH. The resulting membrane delivered outstanding AWE performance with current densities of 5.5 A cm −2 using platinum‐group‐metal (PGM) catalysts and 2.2 A cm −2 using PGM‐free catalysts at 2.0 V. Notably, the in situ electrolyzer device based on ISM‐PBI‐FG offers extensive operational flexibility ranging from 40–100 °C and demonstrates record durability in concentrated alkaline conditions, with a voltage decay rate of only 23.5µV h −1 , outperforming most reported AEMs and ISMs.