Preparation, Modification And Application Of Vanadium Batteries With Different Acid-doped PBI Proton Exchange Membranes

As a kind of large-scale energy storage device,vanadium redox flow battery（VRFB）has gained more and more attention and entering the stage of commercialization.The operation of VRFB is dependent on the performance of proton exchange membranes（PEMs）,at present,Nafion membranes（DoPont）are now in common used in VRFB.However,its high cost and high vanadium permeability have curbed their application and development.Polybenzimidazole（PBI）has the ability of proton conduction and excellent resistance to vanadium in acidic conditions,but the proton conductivity still needs to be improved.In this paper,a series of PBI PEMs were prepared according to the proton transfer mechanism by means of blending and acid doping methods.The main contents are as follows:1.The molecular structure of PBI is characterized in detail.PBI/PVP membranes are directly prepared by blending.Influences of different PVP content are studied.The results showed that the addition of PVP effectively increased the water absorption,acid doped level and proton conductivity.The PBI-PVP-5 membrane exhibited a high bonded acid level of 2.47 mmol·g^-1 and proton conductivity of 4.81 mS cm^-1,besides,its selectivity(3.12 ×105 S·min·cm^-3)is twice as much as the original PBI membrane(1.12X l05 S ·min cm^-3).In single cell tests,the value of VE（74.15%）and EE（74.59%）at 100 mA·cm-2 increased by 10.06%and 10.75%respectively compared with the original PBI membrane.The self-discharge time of PBI/PVP-5 membrane（307 h）proverb that it can be effectively applied to VRFB system.2.A series of novel PEMs,based on PBI doped with different acids such as methanesulfonic acid（MSA）,phosphoric acid（H3PO4）,sulfuric acid（H2SO4）,and formic acid（HCOOH）,were employed and investigated in VRFB.The proton conductivity of PBI-MSA membrane can reach 10.94 mS cm^-1.After 100 cycles at 100 mA cm-2,the values of CE,VE and EE were 99.65%,81.78%and 81.30%,respectively.After 500 cycles,the EE value remained above 80%with good cycle performance,and the voltage did not decrease significantly after the discharge of 300 h,which is much longer than that of Nafion 115.3.3,3’-diaminobenzidine（DAB）and 4,4’-Dicarboxydiphenylether（DCDPE）were polymerization to synthesize OPBI with one ether bond.H2SO4 doped OPBI membranes were prepared and used in VRFB.The boned acid of OPBI can reach 2.92 mmol·g^-1,and proton selective(2.16×105 S·min·cm^-3)has reached 4.32 times of Nafionl15(0.50×105 S min cm^-3);at the current density of 50 mA cm-2 and 100 mA cm-2,the values of CE and EE can reach 97.28%,98.87%,87.35%and 79.66%respectively.There is no obvious change in cell performance after 100 cycles.The self-discharge time of OPBI（1003 h）is 22.29 times than that of Nafion115（45 h）.