Investigation On The Preparation And Performances Of Thin Film Composite Membrane Of High Stablity For Vanadium Redox Flow Battery

As a non-polluting and highly reliable energy storage system,vanadium redox flow battery(VRB)can be combined with renewable energy generation with large fluctuations in energy output.At present,the price of commercial Nafion membranes is high,which limits the large-scale promotion and application of vanadium redox flow battery.Therefore,developing low-cost and high-performance separators for VRB is of practical significance.Porous membrane does not contain ion exchange groups and less likely to be degradated,thus it has good stability.However,its proton conductivity and ion selectivity are difficult to be balanced.Thin film composite(TFC)membranes prepared by interfacial polymerization can effectively overcome this disadvantage.The traditional polyamide thin film composite(TFC)membrane contains an amide bond which is susceptible to H+ nucleophilic attack,and thus does not tolerate the strong acid and strong oxidizing environment of the VRB.In this paper,polydopamine(PDA)was adopted to improve the chemical stability of polyamide TFC membrane.The experiments show that the PDA layer can effectively protect the polyamide layer from H+ nucleophilic attack.In the chemical stability test,the loss rate of vanadium permeability coefficient is reduced from 8.34% to 4.65%,which is equivalent to the Nafion 115 membrane.Although the polyamide TFC membrane modified by PDA can enhance the chemical stability,it will increase the area resistance of the membrane.Therefore,this paper attempts to prepare another kinds of TFC membranes which can keep stable in the VRB.The polypyrrole TFC membrane prepared by interfacial polymerization with ferric chloride and pyrrole as a two-phase monomer is first evaluated in the VRB.In the chemical stability test,the loss rate of vanadium permeability coefficient is 4.02%,which is smaller than that of the Nafion 115 membrane of 4.33%.The battery test results show that the polypyrrole TFC membrane has an energy efficiency(EE)of 88.7% at current density of 40 m A cm-2,which is 7.0% higher than that of the Nafion 115 membrane.The EE is 81.4% at current density of 80 m A cm-2,which is 5.0% higher than that of the Nafion 115 membrane.The EE can be maintained at about 80% during 100 cycles of charge and discharge.Polyamine TFC membrane prepared by interfacial polymerization of polyethyleneimine and cyanuric chloride as two-phase monomer is also investitaged for VRB.The molecular structure of polyamine does not contain strong electronegative carbonyl and is tolerant to extreme p H.In the chemical stability test,the loss rate of vanadium permeability coefficient is 4.18%,which is also smaller than that of the Nafion 115 membrane.The battery test results show that the polyamine TFC membrane has an EE of 85.7% at current density of 40 m A cm-2,which is 4.0% higher than that of the Nafion 115 membrane.The EE is 80.0% at a current density of 80 m A cm-2,which is 5.0% higher than that of the Nafion 115 membrane.The EE can be maintained at about 79% during 100 cycles of charge and discharge.Finally,this paper analyzed the price and performance of porous composite membranes.Results prove that the porous composite membrane have broad prospects in VRB compared with that of commercial Nafion 115 membrane due to their low cost and superior performances.