Research progress on crown‐ether‐ and cryptand‐functionalized ion exchange membranes for electrochemical devices

As a core material for electrochemical energy conversion, ion exchange membranes occupy a critical position in strategic technological fields such as fuel cells, water electrolysis and electrodialysis. Their functional optimization directly impacts the performance enhancement of electrochemical energy devices. In the modification research of ion exchange membranes, crown ether functional groups, owing to their ability to form hydrogen bonds and enhance membrane–metal ion interactions, have become an effective strategy for optimizing membrane properties including ion selectivity, ionic conductivity and hydrophilicity. To date, crown‐ether‐modified functional membranes have been applied in various electrochemical systems, including anion exchange membrane water electrolysis, anion exchange membrane fuel cells, high‐temperature proton exchange membrane fuel cells and electrodialysis. However, the insufficient complexation stability of crown ethers toward cations limits the long‐term stability of the host–guest structure. Cryptands, as three‐dimensional derivatives of crown ethers, possess a more compact cavity and additional coordination sites due to the introduction of a third bridging arm, resulting in complexation constants for matched guests that are 2–4 orders of magnitude higher than those of crown ethers. This review systematically summarizes the application progress of crown‐ether‐based ion exchange membranes in water electrolysis, fuel cells and electrodialysis, and also reviews the current preliminary research status of cryptand‐based ion exchange membranes in water electrolysis and fuel cells.