Anisotropic Polybenzimidazole Ion‐Solvating Membranes Composed of Aligned Nano‐Sheets for Efficient Acid‐Alkaline Amphoteric Water Electrolysis

Abstract Acid‐alkaline amphoteric water electrolysis (AAA‐WE) can produce green hydrogen under reduced voltage and energy consumption. However, its conflicting demands on ion exchange membranes to have both high ionic conductivity and barrier properties between H + and OH − have thwarted its own development. Here, the preparation of anisotropic polybenzimidazole (PBI) ion‐solvating membrane (ISM) made of hundreds of 28 nm thick nano‐sheets (PBI‐aNS) from gel state PBI (PBI‐Gel) membranes via 2D‐polarized/1D shrinking process, in which loosely packed multi‐layer PBI nano‐fibrous assemblies are shrunken into hundreds of layers of tight 28 nm thick nano‐sheets, is reported. The resulting PBI‐aNS membranes possess excellent dual‐ion conductivity (H + and OH − ), good acid/alkali barrier capability, and robust mechanical properties. Acid‐alkaline amphoteric water electrolysis (AAA‐WE) using PBI‐aNS separators achieves a high current density of 1 A cm −2 at 1.4 V (with iR‐correction) under a voltage increasing rate of 6.1 mV h −1 . This newly designed ISM will lead to new possibilities for the development of next‐generation water electrolysis devices with improved green hydrogen production efficiencies.