Sulfonated poly(ether ether ketone)/poly(vinylidene fluoride)/tungstophosphoric acid membrane for vanadium redox flow battery application:

A blend membrane consisting of sulfonated poly(ether ether ketone), poly(vinylidene fluoride), and tungstophosphoric acid (denoted as SPEEK/PVDF/TPA membrane) has been fabricated and firstly used as ion exchange membrane for vanadium (V) redox flow battery (VRB) application. This composite membrane is characterized by physical and electrochemical methods. The results show that the SPEEK/PVDF/TPA membrane possesses significantly high ion selectivity and low permeability of V(IV) compared with the Nafion 117 membrane. Also VRB single cells with SPEEK/PVDF/TPA membrane show significantly lower capacity loss, higher coulombic efficiency (CE > 93%) and higher energy efficiency (EE > 80%) than that with Nafion 117 membrane. In the self-discharge test, the cells with the SPEEK/PVDF/TPA membrane show better durability. With all the good properties and low cost, the SPEEK/PVDF/TPA membrane shows promising prospects for application in VRB.