Hydrogel-reinforced naphthyl-based polybenzimidazole ion-solvating membranes for optimized performance of alkaline water electrolysis

Alkaline water electrolysis (AWE) requires separators with high ionic conductivity to ensure high efficiency in hydrogen production. While naphthyl-based polybenzimidazole (NPBI) ion-solvating membranes exhibit excellent alkaline stability, their dense morphologies limit electrolyte uptake and hydroxide conductivity. To overcome this limitation, we developed a hydrogel-reinforced NPBI composite membrane (NPBI-PAM-x) through in-situ thermal-induced free radical polymerization of acrylamide within NPBI polymer matrix. The resulting membranes featured with an asymmetric dual-layer architecture, where a porous polyacrylamide (PAM) hydrogel facilitated KOH absorption and ion transport, while a dense NPBI layer provided mechanical integrity and gas barrier properties. This unique structure enabled the NPBI-PAM-1.5 membrane to achieve a hydroxide conductivity of 163.7 mS cm −1 in 6 M KOH at 80 °C, which was substantially higher than that of pristine NPBI (118.9 mS cm −1 ), while also exhibiting controlled swelling and low gas permeability. NPBI-PAM-1.5 retained 90.1 % of its initial conductivity following a demanding 3200 h alkaline stability test in 6 M KOH at 80 °C. This result demonstrated the NPBI-PAM-x membrane materials’ excellent resistance to chemical degradation. In a single zero-gap alkaline water electrolyzer at 80 °C, the NPBI-PAM-1.5 membrane achieved a current density of 1.41 A cm −2 at 2.0 V using non-precious metal electrodes, and the current density increased to 1.65 A cm −2 at 90 °C. Furthermore, the single AWE device operated stably for 428 h at 500 mA cm −2 and 80 °C. This work demonstrates that incorporating a hydrophilic hydrogel into a chemically stable NPBI polymer matrix is an effective strategy to enhance the performance of NPBI-based ion-solvating membranes for AWE, offering a practical approach to advance green hydrogen production.