Preparation And Performance Of Proton Exchange Membranes For Acid And Alkali In All Vanadium Redox Flow Batteries

All-vanadium redox flow battery has been the best choice of energy storage system due to the advantages of high charge-discharge efficiency,long service life,green safety and low price.The proton exchange membrane is one of the core omponents of the vanadium redox flow battery,which determines the energy efficiency and service life of the vanadium battery.Now,the commercial proton exchange membrane for vanadium battery are the Nafion series,which limit the vanadium battery commercialization due to its high price,high vanadium ion permeability.So,developing PEM with a high structure-property and low cost is necessary for pushing the commercialization process of VRB systemSulfonated poly(ether ether ketone),SPEEK)proton exchange membrane possess advantages of low cost,high selectivity and simple preparation.As a kind of membrane material for vanadium battery application,the VRB performance is highly dependent upon their sulfonated degrees.SPEEK with low sulfonated degrees lead to the proton conductivity is low;SPEEK with high sulfonated degree lead to high water uptake and vanadium ion permeability.In this paper,we prepared SPEEK/functionalized graphene oxide composite membranes and studied the relationship of performance and structure of composite membranes.We report a novel SPEEK/PPD-GO hybrid membrane,in which p-phenylene diamine-functionalized graphene oxide(PPD-GO)are involved into SPEEK matrix,the structure and properties of the composite membranes were characterized and tested.It was found that the acid-base ion pair formed at the interface between PPD-GO and SPEEK matrix reduced the swelling rate and vanadium ion permeability,and composite membranes possess high proton conductivity at the same time.The SPEEK/PPD-GO-1 membrane exhibited best performance than that of other composite membranes at the current density of 30 mA·cm-2.And the SPEEK/PPD-GO-1 membrane possess higher coulomb efficiency(96.9%vs 91%)and energy efficiency(82.8%vs 66.8%)than those of Nafion 117 membrane.The SPEEK/PPD-GO-1 film has good acid resistance and chemical stability even though after 300 charge-discharge cycles.ODA-AN-GO with nitrogen content(3.04%)was prepared by chemical modification and SPEEK/ODA-AN-GO composite membranes were prepared.The results show that the increase of amino groups in the composite membrane enhance the effect of the acid-base ion pairs on the composite membrane,and the enhanced acid-base interaction enhances the proton conductivity of the composite membrane.SPEEK/ODA-AN-GO-2 possess the best performance than that of other composite membranes and the coulomb efficiency and energy efficiency of the battery were stable after 300 times of single cell cycles.