Recent advances in ion exchange membranes for water electrolysis

Abstract

As the key component of water electrolysis (WE), ion exchange membranes (IEMs) determine the energy efficiency, gas purity, and device durability. A typical IEM provides conductivity through its hydrated ion transport channels. However, the same channel is also responsible for water absorption, membrane swelling, and gas crossover. Therefore, recent membrane research has moved from maximizing conductivity toward controlling the chemical and structural environment in which ions, water, and gases move. This review covers this shift across proton exchange, anion exchange, ion-solvating, and bipolar membranes. The influence of polymer backbones, ionic or solvating groups, confined channels, and reinforced architectures on membrane conductivity, dimensional stability, gas separation, and chemical durability are discussed. We further provide perspectives on why device-level durability cannot be inferred from ex situ membrane stability, since water distribution, gas evolution, electrode contact, and heat accumulation in operating cells can introduce additional failure modes.