Nanoscale Solid Superacid-Coupled Polybenzimidazole Membrane with High Ion Selectivity for Flow Batteries
Lei Hu, Yue Du, Gao Li, Mengting Di, Ning Zhang, Yu Pan, Xiaoming Yan, Baigang An, Gaohong He
Abstract
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.