Nanoscale Solid Superacid-Coupled Polybenzimidazole Membrane with High Ion Selectivity for Flow Batteries

Nanoscale solid superacid SO42–/ZrO2/WO3 is coupled into imidazole-hydroxyl-quaternary ammonium co-functionalized polybenzimidazole (PG112) to address the trade-off effect of membrane for large-scale flow battery application. Nanoscale SO42–/ZrO2/WO3 particles with high sulfonic groups are dispersed in membrane as redox-active ion barriers and proton carriers, which mitigate the electrolyte crossover and maintain high ion conductivity. The VO2+ permeability of the prepared membrane (7.86 × 10–10 cm2 s–1) is significantly lower than those of PG112 (3.93 × 10–9 cm2 s–1) and Nafion 212 (7.76 × 10–8 cm2 s–1) membranes. The vanadium flow battery with this membrane exhibits a longer self-discharge duration time of 231 h compared with Nafion 212 (35 h) and PG112 (88 h) membranes. High coulombic efficiencies of 97.5–99.2% at 40–120 mA cm–2 are obtained for the prepared membrane, which are higher than those for Nafion 212 (78.0–92.8%) and PG112 membranes (96.2–98.6%). Stable cycle performance and low retention capacity are also observed, suggesting the excellent chemical stability of the prepared membrane in vanadium flow battery operation. This work provides a prospective and applicable membrane to enhance the performance of flow battery.