Study On Preparation Of Amphoteric Membrane For Vanadium Redox Flow Battery By Atom Transfer Radical Polymerization

Vanadium redox flow battery?VRB?attracts more and more researchers to explore it because of its many advantages.At present,membrane is one of the cyucial key materials to improve the performance of VRB,which determines the battery cycle performanc and efficiency.The cost of membrane can account for 20% of the whole battery system,so it is of great significance for VRB to reduce the price of membrane and improve the performance of membrane.At present,the commercial membrane used in VRB is mainly perfluorosulfonic acid ion exchange membrane produced by Du Pont Company,such as Nafion.Nafion has high chemical stability and high proton conductivity,however Nafion is expensive and its vanadium ion permeability is high,which limits its large-scale application in VRB.In this study,the surface of Nafion membrane was modified by atomic transfer radical polymerization?ATRP?to overcome the disadvantage of high vanadium permeability of Nafion when used in VRB.Different proportions of amphoteric groups on the surface of Nafion was introduced by ATRP methd to ensure high proton permeability and low permeability.Furthermore,in order to reduce the price of membrane for VRB,chloromethylation of polysulfone?PSF?membrane was modified by ATRP to explore a new type of amphoteric membrane.First,the contact angle of amphoteric ion exchange membranes mixed with Nafion-g-PSBMA resin and Nafion resin,Nafion-g-PNaSS resin?Nafion-g-PMETAC resin and Nafion resin were measured.The thermogravimetric analysis and XPS test of Nafion-g-PNaSS resin?Nafion-g-PMETAC resin and Nafion resin were carried out.The results show that the hydrophilicity of the two ion exchange membranes is improved,and the thermal stability of Nafion is changed by NaSS and METAC.Secondly,in order to improve the properties of Nafion membrane on VRB,ATRP reaction was carried out on the surface of Nafion115 and Nafion212 membranes.NaSS and DMAEMA were grafted at a ratio of 4:1,Nafion115-g-P?DMAEMA-co-NaSS?and Nafion212-g-P?DMAEMA-co-NaSS?were obtained.The results show that the average energy efficiency?EE?value of Nafion115-g-P?DMAEMA-co-NaSS?is 87.26%,when the current density is 40⁸0 m A?cm^-2,which is 7.32% higher than the average EE?79.94%?of Nafion 115.When the current density is 40⁸0 m A?cm^-2,the average EE of Nafion212-g-P?DMAEMA-co-NaSS?is 82.94%,which is 9.04% higher than the average EE of the Nafion212?73.9%?.It is proved that the surface grafted of NaSS and DMAEMA on Nafion can improve their application in VRB.In order to further reduce the cost of VRB membrane,the grafting of anionic and cationic monomers onto chloromethylated polysulfone?CMPSF?was studied.Comparing the degree of chloromethylated polysulfone(0.62 mmol?g^-1)when SnCl₄ as a catalyst with the degree of chloromethylated polysulfone(0.16 mmol?g^-1)when ZnCl₂ as a catalyst,and the SnCl₄ was finally chosen for its high catalytic effect.By comparing the energy efficiency of VRB with different reaction time,the results show that the average energy efficiency?60.38%?of the amphoteric membrane with the current density of 40⁸0 m A?cm^-2 and the reaction time of 4 h is higher than the average energy efficiency of the blank?52.92%?.The optimum reaction time?4 h?of the grafting of NaSS and DMAEMA was established,and the physicochemical properties and electrochemical performance of several base membranes were tested.The results show that VRB has the highest average energy efficiency?81.08%?when the current density is 40⁸0 m A?cm^-2,when the blending ratio of 1:1 for CMPSF and PSF,which was 4.54% higher than that of PSF?76.54%?under the same conditions.The self-discharge tests were carried out after grafting different proportion NaSS and DMAEMA of the mixed membrane.It was found that with the increase of DMAEMA content,the self-discharge time of the battery also increases gradually,up to 28 h.It is about 200% higher than untreated membrane,and nearly 162% higher than the Nafion212 self-discharge time.