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

Abstract 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.