In Situ Crosslinked Diallylammonium‐Functionalized Poly(Biphenyl Alkylene) for High‐Performance Anion Exchange Membranes

The intrinsic trade-off between ion conductivity and mechanical integrity in high-ion exchange capacity (IEC) anion exchange membranes (AEMs) has remained a major challenge for the practical implementation of anion exchange membrane water electrolyzer (AEMWE) technology. Here, crosslinked AEMs (BP-cross-PDAA) is developed via free-radical cyclopolymerization of diallylammonium-functionalized poly(biphenyl alkylene), where the IEC (n) is precisely tuned from 2.32 meq g^-1 to 3.39 meq g^-1 by adjusting the content of diallyldimethylammonium comonomer. BP-cross-PDAA membranes exhibited excellent hydration characteristics, including hydroxide conductivity (up to 152.4 mS cm^-1 at 80 °C), swelling ratio (24.2%), and alkaline stability (98.7% retention over 350 h), attributed to their robust crosslinked network structure without sacrificing their high IEC. Furthermore, membrane-electrode assembly (MEA-n) tests demonstrated remarkable AEMWE performance, with MEA-3.39 achieving a peak current density of 12.39 A cm^-2 at 2.0 V using a non-platinum group metal anode, and 6.1 A cm^-2 under pure water condition. MEA-3.39 also exhibited excellent durability, with a minimal voltage degradation rate of 1.2 µV h^-1 over 1,000 h at 1 A cm^-2 in 1 M KOH at 50 °C.