Study On The Preparation And Characterizations Of Novel Membrane Based On Nafion For Vanadium Redox Flow Battery Application

All-vanadium redox flow battery (VRB) has many advantages such asindependently tunable between capacity and power, long cycle life and deepdischarge capability. It can be widely used in large scale energy storage and peakload regulation. Ion-exchange membrane is the bottleneck of VRB. Nafion (Dupont)is usually used as ion-exchange membranes in the VRBs, but its high price andserious vanadium penetration restrict the further application of Nafion in the VRBs.Therefore, how to reduce the cost as well as improving the performances of Nafionused in VRB has great practical significance.With the purpose of reducing the cost and improving the vanadium-blockingperformance of Nafion, polytetrafluoroethene/Nafion(PTFE/Nafion, P/N) compo-site membranes with different thickness were prepared by casting Nafion solutionon the relatively cheaper porous PTFE membrane. The physical and chemicalparameters, microstructure, electrochemical performances and cell performances ofthese composite membranes were tested, respectively. The results showed that thevanadium-blocking performance of the25μm-thick P/N composite membrane was12.6percent higher than that of the Nafion212membrane. Furthermore, the energyefficiency of the45μm-thick P/N composite membrane was increased by7.8percent at the current density of40mA/cm2.In order to investigate the influence of the microstructure change of Nafion onits performances, different kinds of the surfactants were applied to prepare therecast Nafion membrane. And as far as we know, it was the first time that thesurfactants were used to modify the membranes for VRB application. Thecomposite membranes with different contents of perfluorinated surfactant and thecomposite membranes with5%mass fraction of conventional surfactants wereprepared. The physical and chemical parameters, microstructure, electrochemicalperformances and cell performances of these composite membranes were tested,respectively. The results showed that perfluorinated surfactant effectively improvedthe vanadium-blocking performance of the composite membranes, and theconductivity of the composite membranes was also increased. In addition, thewater-blocking performance of the composite membranes with the conventional cationic surfactants was improved, and the water content and electrical conductivityof the composite membranes with the conventional anionic surfactants was alsoincreased. Moreover, compared with blank Nafion membrane, the energy efficiencyof the composite membranes with5%mass fraction of perfluorinated surfactantwas increased by12.6percent at the current density of40mA/cm2, and the energyefficiency of the composite membranes with5%mass fraction of nonionicsurfactant was increased by6.7percent at the current density of40mA/cm2.Finally, the development situation and the prospect of the global energystorage market were analyzed, and the performance and cost of various energystorage batteries were compared. And the result showed that the PTFE/Nafioncomposite membranes could reduce the cost of the VRB membrane effectively.