Asymmetric Porous Ion-Solvating Membranes with a Well-Defined Two-Layer Structure for High-Efficiency Alkaline Water Electrolysis

Abstract Poly(oxindole biphenylene) ion-solvating membranes (POBP-ISMs) have emerged as promising candidate membrane materials for use in hydrogen production through alkaline water electrolysis (AWE), owing to their exceptional alkaline stability. However, their dense architecture leads to insufficient exposure of functional groups, resulting in low electrolyte uptake and substantial ion transport resistance, which collectively limit ionic conductivity and compromise the durable, high-efficiency performance of AWE. To overcome this limitation, we prepared an asymmetric porous POBP (AP-POBP) membrane using a two-step nonsolvent-induced phase separation (NIPS) method. The AP-POBP membrane has a two-layer structure, including a thin and dense surface layer and a highly porous support layer. This unique structure simultaneously enhances ionic conductivity, superior gas barrier, and high chemical stability performance of ISMs. Noticeably, the Ni-based AWE with the obtained AP-POBP ISM achieved a high current density of 2.4 A cm−2 at 2.0 V, superior to that of a dense membrane (0.25 A cm−2). It maintained stable operation for 800 h at 2 A cm−2 with no appreciable membrane degradation. These results demonstrate that the introduction of an asymmetric porous two-layer architecture represents a simple yet effective strategy for designing advanced ISMs with precisely controlled porous morphologies, enabling superior comprehensive performance in AWE applications.