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. Quaternized 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 Nafion117 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 Nafion117 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.

Poly(phthalazinone ether ketone ketone) anion exchange membranes with pyridinium as anion exchange groups (PyPPEKK) were prepared by reacting chloromethylated poly(phthalazinone ether ketone ketone) membranes with pyridine in solution. The reaction conditions including diluent solvents, pyridine concentration, reaction time and temperature were investigated. Under the optimized reaction condition, PyPPEKK anion exchange membranes with IEC values in the range of 0.96–1.55 mmol g⁻¹ and water uptake in the range of 10.2–16.5% were obtained. The swelling ratio of PyPPEKK membranes in deionized water and VOSO₄ solution were in the range of 3.2–10.6% and 2.5–7.8%, respectively. PyPPEKK membranes showed good chemical stability in VO₂ ⁺ solution. Notably, PyPPEKK membranes had higher coulombic efficiencies of VRB and much lower vanadium permeability compared with Nafion117 membrane. The energy efficiency of VRB with PyPPEKK membrane reached 83.6% at 80 mA cm⁻² while the energy efficiency of VRB with Nafion117 membrane was 80.7% at the same charge–discharge current density. Furthermore, PyPPEKK membrane exhibited good performance in the 100-cycle charge–discharge VRB test.