Preparation And Performance Of Polybenzimidazole Composite Membrane For Vanadium Redox Flow Battery

With environmental pollution and decreasing energy sources,the development of sustainable energy,green energy and renewable energy has become a research hotspot pursued all over the world.As a new type of renewable energy,all-vanadium oxide flow battery(VRFB)has attracted much attention due to its advantages of long service life,high safety and low cost.As the core component of VRFB,the proton exchange membrane determined the efficiency and service life of the entire battery.At present,commercial Nafion series membranes are commonly used separators in flow batteries,but the high price and high vanadium transmittance limits their commercial use in VRFBs.Polybenzimidazole(PBI)proton exchange membrane has a good application prospect in VRFB,but its proton conductivity still needs to be improved.In this paper,a sulfonated polybenzimidazole(s PBI)with a controllable degree of sulfonation was synthesized by introducing monomers.The best performing sulfonated polybenzimidazole was selected by comparison.Ui O-66 was added to it,because of the pore size of MOF is between hydronium ions and hydrous vanadium ions.Adding this MOF structure not only improves the vanadium permeability of the composite membrane,but also increases the proton conductivity of the membrane,ion selectivity increases was increased,and the 50-s PBI-Ui O-5 composite membrane has better energy efficiency at current densities of 40-200m A·cm^-2.Compared to Nafion117 membrane,it still maintains stable charge-discharge performance after 200 cycles under the same current density.In order to improve the proton conductivity of the membrane,an asymmetric membrane of sulfonated polybenzimidazole(s PBI)and polyacrylamide(PAM)was also prepared,and the vanadium permeability was reduced by grafting flexible side chains to s PBI.Experiments show that this asymmetric membrane has high proton conductivity and low vanadium transmittance.Compared with Nafion117,s PBI₃₀-PAM has a higher current density of 40-150 m A·cm^-2,high energy efficiency and exhibited long-term charge-discharge performance.