Preparation And Performance Study Of Polysulfone Amphoteric Membrane For Vanadium Redox Flow Battery

Vanadium redox folw battery(VRB)is widely used for large-scale energy storage technology because of its low cost,safety and stability,long life,environmental friendliness and good battery uniformity,and its charge and discharge status can be monitored in real time.The main shortcoming that restricts the rapid development of VRB is the membrane.In this paper,a new type of amphoteric ion exchange membrane was prepared by the atom transfer radical polymerization method(ATRP)and its performance in VRB was studied.The orthogonal experiment method was used to optimize the three paramenters that affect the polysulfone chloromethylation including reaction temperature,time and catalyst dosage.The optimal reaction conditions were screened out as follows:reaction temperature is 60?,reaction time is 16 h,and the amount of catalyst Sn Cl₄is 0.2 mol L^-1.The dense skin chloromethylated polysulfone(CMPSF)porous base film was prepared by the two-gel bath phase conversion method,and the influence of the immersion time in n-pentanol on the base film was studied.The CMPSF dense film was also prepared by solvent casting method and compared with the porous membranes with asymmetric structures.The surface resistance,conductivity and water flux tests show that the optimal base membrane is M-10s with the immersion time of 10s in n-pentanol.Sodium p-styrene sulfonate(NaSS)and dimethylaminoethyl methacrylate(DMAEMA)on the M-10s base membrane to prepare an ion exchange membrane with asymmetric structure.Two methods i.e.single grafting and hybrid grafting of the monomers were used.It is found that the performance of the hybrid grafting membrane is better than that of the single grafting membrane.When the grafting ratio of C_NaSS:C_DMAEMA=4:1,the membrane exhibits a high conductivity of 74.1 m S cm^-1,a low permeability of vanadium ions and excellent ion selectivity.And the average energy efficiency value of VRB with M-4:1 membrane is 89.79%,which is 15.27%higher than that of N 212 membrane(74.52%),and the self-discharge time of M-4:1 is160 h,which is much higher than that of N 212.It proves that the performance of the modified membrane is significantly improved,and it also proves that the grafted membrane makes the M-10s base membrane has a high battery performance.Nafion-g-P(NaSS-co-METAC)ion exchange membrane is prepared by grafting NaSS and methacryloxyethyltrimethylammonium chloride(METAC)on Nafion resin by bulk ATRP modification.The reslut shows that the modified M-1:1 membrane has a lower vanadium ion permeability and higher ion selectivity than the N 212membrane,and the self-discharge time of the M-1:1 membrane is 54 h,which is much longer than that of N 212 membrane.