LAUSR

Abstract A series of novel sulfonated poly(phthalazinone ether ketone)s containing pendant phenyl moieties (SPPEK-Ps) are synthesized and thoroughly characterized. The chemical structures of the polymers are confirmed by 1 H NMR and FTIR analysis. The physicochemical properties and single cell performance of SPPEK-P membranes are systematically evaluated, revealing that the membranes are thermally, chemically and mechanically stable. The area resistances of SPPEK-P-90 and SPPEK-P-100 are 0.75 Ω cm 2 and 0.34 Ω cm 2 , respectively. SPPEK-P membranes are impermeable to the bulky hydrated VO 2+ ion and exhibited low V 3+ ion permeability (SPPEK-P-90, 2.53 × 10 −5  cm min −1 ) (Nafion 115 membrane: 9.0 × 10 −4  cm min −1 ). Tests of SPPEK-P-90 in vanadium redox flow batteries (VRFBs) demonstrate a comparable columbic efficiency (CE) and energy efficiency (EE) to that of Nafion 115, where the CE is 98% and the EE is 83% at 60 mA cm −2 . Moreover, the SPPEK-P-90 membrane exhibits stable performance in cell over 100 charge-discharge cycles (∼450 h).