Poly(tetrafluoroethylene) reinforced sulfonated poly(ether ether ketone) membranes for vanadium redox flow battery application

► Sulfonated poly(ether ether ketone) was reinforced by porous PTFE. ► SPEEK/PTFE membrane has a lower swelling ratio than pristine SPEEK. ► The ion selectivity of SPEEK/PTFE membrane is higher than SPEEK in VRB tests. ► SPEEK/PTFE membrane shows much higher stability than SPEEK.