Anion exchange membranes from brominated poly(aryl ether ketone) containing 3,5-dimethyl phthalazinone moieties for vanadium redox flow batteries

摘要

A series of heterocyclic poly(aryl ether ketone)s containing 3,5-dimethyl phthalazinone moieties were synthesized via the copolymerization of 4-(3,5-dimethyl-4-hydroxyphenyl)(2H)-phthalazin-1-one, 4-(4-hydroxyphenyl)(2H)-phthalazin-1-one and 4,4'-difluorobenzophenone. The resulting polymers were brominated with N-bromosuccinimide as the bromination reagent. Brominated poly(phthalazinone ether ketone) (BPPEK) with a degree of substitution in the range of 0.48-0.82 was obtained. Quatemized poly(phthalazinone ether ketone) anion exchange membranes (QBPPEK) were prepared from BPPEK membranes with trimethylamine as the amination reagent, ion exchange capacity (IEC) values of the QBPPEK membranes were in the range of 0.82-1.53 mmol g~(-1). Compared with Nafionll7 membrane, QBPPEK membranes showed much lower vanadium permeability. Coulombic efficiencies of the vanadium redox flow battery (VRB) with QBPPEK membranes were higher than that with the Nafionll7 membrane. The energy efficiency of the VRB increased with an increase in the IEC of the QBPPEK membrane. The energy efficiency of the VRB cell with the QBPPEK membrane having an IEC of 1.53 mmol g~(-1) was 88%, which was higher than that of the cell with the Nafion117 membrane. During 100 charge-discharge cycles, the QBPPEK anion exchange membrane showed a stable performance.