Study On Preparation And Performance Simulation Of Porous Membranes For Vanadium Redox Flow Battery

Large-scale energy storage technique has become the main bottleneck for improving the utilization ratio of renewable energy in China's power grid.All vanadium redox flow battery(VRB)is considered to be one of the candidates of the most promising large-scale energy storage system due to its high efficiency,scalability,and safety.However,the problems of low ion selectivity,high cost,difficulty in balancing conductivity and vanadium permeability of Nafion membranes for VRB have prevented the wide commercialization of VRB.Therefore,this paper aims to develop the membrane with excellent ion selectivity,low cost and good chemical stability for VRB.By means of interfacial polymerization,a layer of polyamide is polymerized on the surface of the polyethersulfone(PES)membrane to form a thin film composite(TFC)membrane.In order to further improve the stability of the polyamide TFC membrane,polydopamine was used to form a more stable VRB TFC membrane.Through the porosity and water flux test,M₀-7 with the lowest water flux is selected as the base membrane for the subsequent process.And the successful preparation of polydopamine modified polyamide TFC membrane was prove by SEM and XPS characterization.After modification with polydopamine,the average radius of the membrane is 0.24-0.25nm,which can effectively block vanadium ions and penetrate hydrogen ions.TGA and tensile testing prove that the thermal stability and mechanical properties of the polyamide TFC membrane modified by polydopamine are higher than those of PES-based membrane and polyamide TFC membrane.The N element distribution of EDX proves that the polydopamine modified polyamide TFC membrane has high chemical stability.Based on experimental research,a mathematical model was adopted to simulate the operation of a all vanadium redox flow battery.With reference to existing models,a two-dimensional,transient,and isothermal model was established to simulate and study the transmission mechanism of various ions in the electrolyte through the porous membrane with pore sizes of 0.35,0.50,0.65 and 0.80 nm during VRB operation.The effect of the pore size on the battery performance and the transportation mechanism of vanadium ions are discussed.It can be concluded from the simulation that the decrease of the pore size of the porous membrane effectively inhibits the penetration of vanadium ions.The transmission mechanism of vanadium ions through the porous membrane of0.35,0.50,0.65 and 0.80 nm is mainly diffusion and migration.When the pore diameter is 0.65 nm,the transportation of protons and the cross over of vanadium ions is balanced,with relatively high voltage efficiency and energy efficiency.The cost of polydopamine-modified amide TFC was also estimated and the calculation results show that the polydopamine-modified polyamide TFC membrane has obvious advantages in terms of performances and cost compared with the commercial Nafion 115 membrane.