Anion exchange membranes for electrically rechargeable zinc–air batteries: Structure-transport-degradation relationships and design strategies

Electrically rechargeable zinc–air batteries (ERZABs) are promising for grid and mobility energy storage due to zinc’s abundance, high theoretical capacity, and relatively benign chemistry. A critical component governing their performance is the anion exchange membrane (AEM), which must efficiently conduct hydroxide ions while suppressing zincate crossover and maintaining stability in strongly alkaline environments. This review examines how polymer structure, cation chemistry, water management, and microphase morphology collectively influence hydroxide transport and long-term durability. Particular attention is given to the interplay between ion exchange capacity, water uptake, conductivity, and dimensional stability, as well as the role of membrane microstructure in controlling multivalent ion transport. Advances in membrane fabrication strategies, including crosslinking, blending, pore-filling, and electrospinning, are evaluated in terms of their impact on transport and mechanical integrity. Recent developments in ether-free polyaromatic backbones and sterically protected cations have enabled hydroxide conductivities exceeding 100 mS cm⁻¹ at elevated temperatures with improved alkaline stability. However, many reported values are obtained under fully hydrated conditions and may not directly reflect ERZAB operation, where carbonation, hydration gradients, and cycling stresses influence performance. By linking polymer design to ion transport, degradation behavior, and device-level constraints, this review provides a structured perspective on AEM development and identifies key considerations for achieving durable and efficient ERZAB systems.