Selective Swelling-Induced Tricyclohexylphosphine-Functionalized Adamantane-Containing Poly(aryl ether ketone) Membranes for Vanadium Redox Flow Batteries

High-power-density vanadium redox flow batteries (VRFBs) are essential for large-scale energy storage and require high-conductivity and -selectivity membranes. Tricyclohexylphosphine-functionalized adamantane-containing poly(aryl ether ketone) (TcAPEK) membranes have been synthesized and evaluated in VRFBs for the first time. The TcAPEK-virgin membrane with a low ion exchange capacity of 0.48 mmol g–1 displayed a high area resistance (AR) of 171.9 Ω cm2. After selective swelling-induced treatment, the TcAPEK membranes exhibited outstanding ionic conductivity. The TcAPEK-130 membrane with a low AR of 0.14 Ω cm2 reached comparable to the highly conductive Nafion 212 membrane. TcAPEK membranes, benefiting from Donnan exclusion, could effectively reduce the migration of vanadium ions among the positively charged functional groups and vanadium ions. The TcAPEK membranes demonstrated high mechanical strength, ranging from 45.5 to 46.9 MPa, and good toughness. The TcAPEK-130 membrane yielded impressive energy efficiency (EE = 91.8% at 80 mA cm–2, EE = 85.5% at 200 mA cm–2, and EE = 79.9% at 300 mA cm–2). This work explores the possibility of using anion exchange membranes (AEMs) with quaternary phosphonium groups for VRFB, providing available methods and potential membrane materials for designing and preparing high-performance ion exchange membranes for high-power-density VRFB.