A sulfonated poly(ether ether ketone)/amine-functionalized graphene oxide hybrid membrane for vanadium redox flow batteries
A series of hybrid membranes (SPEEK/PPD-GO) based on sulfonated poly(ether ether ketone) (SPEEK) and p-phenylene diamine-functionalized graphene oxide (PPD-GO) are prepared by a solution-casting method for vanadium redox flow batteries (VRB). The physicochemical properties such as water uptake, swelling ratio, ion exchange capacity, proton conductivity and vanadium ion permeability of SPEEK hybrid membranes are well controlled by the incorporated PPD-GO nanofillers. SPEEK/PPD-GO hybrid membranes show higher coulombic efficiency (CE, 96.9%) and energy efficiency (EE, 82.8%) at 30 mA cm−2 than Nafion 117 membrane (CE, 89% and EE, 72.5%). The self-discharge time of the SPEEK/PPD-GO-1 hybrid membrane (56 h) is longer than that of the Nafion 117 membrane (26 h), demonstrating its excellent vanadium ion selectivity. Moreover, the SPEEK/PPD-GO membrane exhibits a stable operation performance for up to 100 cycles, accompanied with no significant decay in CE and EE. The present experimental results demonstrate that it is a feasible method by controlling the interfacial interaction to realize a high performance hybrid membrane for VRB systems.