Anion-Exchange Membranes with Cryptand-Barium-Based Cations and Diverse Backbones for Water Electrolysis

The highly stable [2.2.2]cryptand was incorporated into tunable polymer backbones of anion-exchange membranes (AEMs) to systematically compare the compatibility of three representative frameworks with the cryptand functional group. The results demonstrated that the AEMs based on polyphenylene (PPO) and biphenyl-based copolymer (BP) backbones exhibited superior overall performance compared to those derived from ring-opening metathesis polymerization (ROMP) of norbornene derivatives. Among them, the BP-135-C-Ba AEM showed the highest OH– conductivity (271 mS/cm at 70 °C) along with satisfactory dimensional stability. When applied in anion-exchange membrane water electrolyzers (AEMWEs), the BP-135-C-Ba-based membrane electrode assembly (MEA) achieved a current density of 1.63 A·cm–2 at 2.0 V, along with good durability. This study confirms that the combination of a BP backbone and cryptand functional group delivers optimal performance, offering a strategy for designing high-performance ion-conducting membranes for energy conversion and storage devices.