A high ion-conductive and stable porous membrane for neutral aqueous Zn-based flow batteries

Abstract Zn-based flow batteries (ZFBs) with low cost and high efficiency have become one of promising energy storage technologies for renewable energy development. However, in ZFBs, an anion exchange membrane (AEM) losses ion conductivity because of the presence of Zn2+. The side reaction of Zn2+ precipitation resulted in ion exchange decomposition of AEM with quaternary groups. While a cation exchange membrane (CEM) hinders anion conductivity because of electrostatic interaction between ion-exchange groups and anions. To address poor ion conductivity of ion exchange membrane in ZFBs, a polyetherimide (PEI)-based porous ion conductive membrane is developed via water phase inversion technology for ZFBs. The ion conductive mechanism is based on pore size exclusion, which mitigates the effects of ion exchange groups on ion conductivity. The membrane performance is further improved by introducing suitable polyvinylpyrrolidone (PVP) and controlling tetrahydrofuran (THF) volatilization time. The results demonstrate that in Zn/4-Hydroxy-2,2,6,6-tetramethyl-piperidine 1-Oxyl (TEMPO-OH) flow battery, a coulombic efficiency (CE) of more than 98% and an energy efficiency (EE) of ~77% was achieved at 20 mA cm−2, and the flow battery assembled with 20PEI-1PVP-90s can stably run for 150 cycles. The PEI-based porous membrane with low cost and high efficiency is considered as a promising strategy for ZFBs.