Low Permeability Membrane Regulated by Main/Side-Chain Bisulfonated Polybenzimidazole and CAU-10-H for Vanadium Redox Flow Batteries

A series of composite membranes (sPBIp3-CAUX) are prepared by using modified sulfonated polybenzimidazole with an optimal side link grafting degree of 30% as a polymer matrix and then doping with CAU-10-H. The hydrophobic alkyl side chains and hydrophilic sulfonic acid groups easily form microphase separated structures due to the polarity difference, which is conducive to the enhancement of proton conductivity. The introduction of CAU-10-H into the polymer effectively prevents the passage of vanadium ions because the vanadium ion transport path becomes more tortuous. The sPBIp3-CAU2 membrane has low vanadium permeability (3.1 × 10–9 cm2 min–1) and excellent ion selectivity (9.16 × 106 S min cm–3). In addition, the sPBIp3-CAU2 membrane shows good cell performance at 60 mA cm–2 with CE of 93.32% and EE of 83.03% compared with those of Nafion 117.