Quaternized membranes bearing zwitterionic groups for vanadium redox flow battery through a green route

Abstract Novel quaternized membranes with zwitterionic groups applied in all-vanadium redox flow battery (VRB) have been prepared using a solvent free strategy, which is environmentally-friendly and different from traditional methods using organic solvents as reaction media. It was performed by dissolving cardopolyetherketone (PEK-C) in monomers mixture of 4-vinylbenzyl chloride (VBC) and divinylbenzene (DVB), and then in situ polymerization to incorporate PEK-C into the network of poly (VBC–DVB). The resulting copolymer was immersed in dimethylamine (DMA) followed by 1,3-propane sultone (PS) aqueous solution to obtain the target quaternized membranes bearing zwitterionic groups ([ CH 2 N + (CH 3 ) 2 CH 2 CH 2 CH 2 SO 3 − ]), which greatly enhance the chain packing density, and consequently improve membrane stability. The optimized quaternized membrane with zwitterionic groups showed a 20% decrease in vanadium ion permeability as compared to the benchmark quaternized membrane without zwitterionic groups. It also possesses good mechanical strength even after immersion in VO 2+ solution for as long as 20 days. Comparing the commercial Nafion117 with the optimized membrane, the vanadium ion permeability sharply decreased from 10.80×10 −5  cm min −1 to 0.21×10 −5  cm min −1 while the coulombic and energy efficiency increased from 89.7% and 68.3% to 97.1% and 73.4% at 50 mA cm −2 , respectively. The present quaternized membrane with zwitterionic groups shows good characteristics for application in VRBs.