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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 À1 and water uptake in the range of 10.2-16.5% were obtained. The swelling ratio of PyPPEKK membranes in deionized water and VOSO 4 solution were in the range of 3.2-10.6% and 2.5-7.8%, respectively.PyPPEKK membranes showed good chemical stability in VO 2 + 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 À2 while the energy efficiency of VRB with Nafion117 membrane was 80.7% at the same chargedischarge current density. Furthermore, PyPPEKK membrane exhibited good performance in the 100cycle charge-discharge VRB test.

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