Sulfonated poly(ether ether ketone) (SPEEK) membranes with different degrees of sulfonation (DS) were fabricated by sulfonation of poly(ether ether ketone) (PEEK) in the concentrated H2SO4 (ca. 98%).Their parameters were obtained and reported

such as the ion exchange capacity (IEC)

area resistance

water uptake and the vanadium ion permeability.The SPEEK membrane with DS of 60% was selected for the vanadium redox flow battery test.It was observed the crystallization of SPEEK decreased

and the ion exchange capacity

water uptake

vanadium ion permeability increased with the DS of SPEEK membranes.The membrane with DS of 60%(SPEEK60) possessed lower permeability of VO2+ ions than that of Nafion117 membrane

the ion selectivity was ten times that of Nafion117 membrane.The VRB single cell with SPEEK60 membrane showed higher coulombic efficiency (CE) and energy efficiency (EE) compared to that with Nafion117.In the self-charge test

the time of SPEEK60 membrane was 2.5 times that of Nafion117 membrane.The performance of VRB with SPEEK membrane can be maintained after cycles test.The SPEEK membrane has a promising prospect for application in VRB.