Thin Film Composite Membranes as a New Category of Alkaline Water Electrolysis Membranes

Abstract Alkaline water electrolysis (AWE) is considered a promising technology for green hydrogen (H 2 ) production. Conventional diaphragm‐type porous membranes have a high risk of explosion owing to their high gas crossover, while nonporous anion exchange membranes lack mechanical and thermochemical stability, limiting their practical application. Herein, a thin film composite (TFC) membrane is proposed as a new category of AWE membranes. The TFC membrane consists of an ultrathin quaternary ammonium (QA) selective layer formed via Menshutkin reaction‐based interfacial polymerization on a porous polyethylene (PE) support. The dense, alkaline‐stable, and highly anion‐conductive QA layer prevents gas crossover while promoting anion transport. The PE support reinforces the mechanical and thermochemical properties, while its highly porous and thin structure reduces mass transport resistance across the TFC membrane. Consequently, the TFC membrane exhibits unprecedentedly high AWE performance (1.16 A cm −2 at 1.8 V) using nonprecious group metal electrodes with a potassium hydroxide (25 wt%) aqueous solution at 80 °C, significantly outperforming commercial and other lab‐made AWE membranes. Moreover, the TFC membrane demonstrates remarkably low gas crossover, long‐term stability, and stack cell operability, thereby ensuring its commercial viability for green H 2 production. This strategy provides an advanced material platform for energy and environmental applications.