Preparation And Properties Of Proton Exchange Membranes For Vanadium Redox Flow Batteries

At present,human urgently needs to vigorously develop new energy.In order to further apply intermittent new energy,energy storage technology gradually shows superior performance.The all-vanadium redox flow battery is favored by researchers because of its advantages,such as large-scale energy storage,rapid response,deep charge and discharge capacity,and long life.As a key component of the all-vanadium flow battery,the membrane should have the characteristics of low vanadium ion permeability,high proton conductivity,low price and friendly environment.At present,the commercial Nafion series membrane is used as the standard membrane for all-vanadium redox flow batteries,but it still has some defects such as high vanadium ion permeability,high price and hard to degrade.Therefore,the non-fluorinated sulfonated membranes has become one of the alternatives to Nafion.In this study,SPEEK was modified by doping the appropriate fillers to reduce the vanadium penetration of the membrane and improve proton conductivity.In this paper,cyclodextrin(β-CD)was added into SPEEK as filler,and the proton conductivity of membrane was improved.By using its complexation reaction,β-CD-HPW complex was formed.The optimum ratio of each filler was determined in this experiment,and the proton conductivity of composite membrane prepared was greatly improved.Then polydopamine coated graphene oxide(DGO)was used to immobilize the complex.UiO-66-NH2 with metal-organic framework(MOFs)was prepared and added to SPEEK.The prepared composite membrane showed a high vanadium inhibition ability,but its proton conductivity was reduced.In the experiment of all-vanadium redox flow battery,the voltage efficiency and energy efficiency of the composite membrane were lower than that of pure SPEEK membrane.C3N4-HPW filler was prepared by hydrothermal method,which not only improved the proton conductivity of the memrane,but also fixed the HPW.When the C3N4-HPW filler is 10 wt%,the vanadium resistance of the composite membrane is basically the same as that of pure SPEEK,but its impedance is greatly reduced.When the current density is 120 mA/cm2,the coulomb efficiency and energy efficiency of the composite membrane reach 98.4%and 87.4%,which is much higher than that of pure SPEEK energy efficiency(84.6%),showing excellent battery performance and promising application in all-vanadium redox flow battery.