Synthesis and characterization of vinylimidazole-co-trifluoroethylmethacrylate-co-divinylbenzene anion-exchange membrane for all-vanadium redox flow battery

The VI-co-TFEMA-co-DVB (VTD) copolymer was synthesized by the solution polymerization of vinylimidazole (VI), trifluoroethylmethacrylate (TFEMA) and divinylbenzene (DVB). The VTD copolymer solution was quaternized with bromoethane (QVTD), and QVTD anion exchange membranes were prepared by the casting method. The chemical structure of the synthesized solution and the thermal stability of the prepared membrane were confirmed by FT-IR, 1H NMR spectroscopy and TGA analysis. The following membrane properties were measured: bursting strength, thermal characteristics, chemical resistance, water content, ion exchange capacity, electrical resistance and ionic conductivity. The maximum values of bursting strength, ion exchange capacity and ionic conductivity were 4.53 kgf/cm2, 1.92 meq/g dry and 0.0088 S/cm, respectively. The minimum values of water content and electrical resistance were 3.33% and 1.25 Ω cm2, respectively. Compared to a commercially available membrane (AMX), the prepared membranes were more chemically resistant. After 150 charge–discharge cycles, the maximum current efficiency, voltage efficiency, energy efficiency and discharge capacity of an all-vanadium redox flow battery were determined to be 94.6%, 79.6%, 75.3% and 47.1%, respectively.