Design and Applications of Polymer Ion Exchange Membranes for Flow Electrochemical Devices

Ion exchange membranes (IEMs) are pivotal components in electrochemical energy technologies such as fuel cells, water electrolyzers, and redox flow batteries. This review systematically analyses recent advances and structure‐performance relationships in IEMs, categorized into cation exchange membranes (CEMs) and anion exchange membranes (AEMs). For CEMs, strategies like inorganic hybridization and microporous polymer design effectively enhance proton conductivity while mitigating fuel crossover and swelling. For AEMs, approaches including ether‐free polymer backbones, side‐chain engineering, and cross‐linked networks improve hydroxide ion conductivity and chemical stability in alkaline environments. The discussion highlights how tailored material design—from perfluorinated and hydrocarbon‐based polymers to emerging covalent organic frameworks—governs device efficiency, durability, and scalability. Finally, future research directions are outlined to overcome existing challenges and accelerate the development of next‐generation IEMs for sustainable energy conversion and storage.