Study On Mass Transfer Through Membrane And Electrolyte Flow Behavior For Vanadium Redox Flow Battery

Vanadium redox flow battery(VRFB)has been widely used in wind or solar energy for battery energy storage,power grid peak shaving and energy storage system for remote transmission with its many advantages such as large-scale,long life,high efficiency,low cost and good safety and so on.It takes different valence state of vanadium ions sulfuric acid solution as the anode and cathode vanadium electrolyte.The ion exchange membrane can not only provide a provision transmission channel for hydrogen ions,but also plays an important part in effectively isolating the active material in the anode and cathode electrolyte.It can also achieve the depth charge and discharge of the battery through the oxidation-reduction electric.In this paper,based on the study of the electrolyte flow and mass transfer behavior in vanadium redox flow battery:UV-VIS Spectrophotometer was employed to investigate the permeation behavior in transmembrane electrolyte ions for quiescent VRFB.Emphasis is placed on the impact on transmembrane osmosis of V02O ions with external factors such as concentration,temperature,state-of-charge(SOC),electric field and osmotic pressure.It was helpful to explore the effects of ion diffusion and side reactions on the capacity loss for VFB by correlating the osmotic coefficient of different vanadium ions.The results indicate that it could increase the energy efficiency and reduce the transfer rate of VO2+ ions by improving the electrolyte concentration;Lowering the system temperature helps inhibit the cross-contamination during long term use and eliminating the side reactions;The osmotic coefficient of VO2+ ions decreased when increasing the SOC;As positive electric field was employed in electrolyte solution,V22+ ions transmembrane diffusion would be accelerated within the aggravation of self-discharge;The osmotic pressure between the anode and cathode acclerates the permeation of V0O,leading to a capacity loss for VFB.The electrolyte stirring or not has a little effect for the vanadium ions permeating across the membrane.In order to inspecte the Nafion117 ion exchange membrane for VRFB with two key performance parameters:permeability and membrane resistance.Testing the behavior of the different velocity for tetravalent vanadium ions electrolyte permeating across the membrane;Using electrochemical testing means,and withing the aid of high-precision battery testing system,helped test the different concentrations of vanadium electrolyte's self-discharge curve.Researching on the battery energy losses for VRFB could help improve the efficiency of battery power.It had very important value in development of the scale application for VRFB;Using ac impedance spectrum determination technology helped establish an evaluation method for ion exchange membrane conductive performance.Based on ac impedance spectra of the membrane resistance measurement technology,it could validate its accuracy and practicability by using sulfuric acid aqueous solution system,magnesium sulfate aqueous solution system,sodium chloride aqueous solution system and the vanadium electrolytic fluid system.On such basis,it could revealate the characteristic of the Nafion117 membrane resistance depending on the vanadium electrolyte solution.Based on Computational Fluid Dynamics(CFD),in order to improve the uniformity of electrolyte distribution and to investigate the fluid flow behavior for vanadium reodx flow battery,it could be equipped with a sloping baffle and a flow weir,which could optimize the structure of traditional straight parallel flow channel.The text discussed about the hydrodynamics characteristics of vanadium electrolyte in sectional form multi-channel of serpentine flow channel.The numerical simulation results showed that:the sectional form multi-channel of serpentine flow channel could not only keep the good uniformity of electrolyte distribution,but also be able to reduce the flowing resistance and the pump consumption.In addition,it could optimize the distribution of electrolyte concentration and improve the battery efficiency by choosing the appropriate flow rate of electrolyte and more uniformity of electrolyte distribution.Discuss the influence of electrolyte flow rate and concentration changing in its properties(density,viscosity,etc.)changing on the flow channel pressure drop resistance.CFD numerical simulation method can effectively control the r&d funds,shorten the test time,improve the efficiency of scientific research,help penetrate inside to the battery to explore the reaction mechanism,easy to optimize the structure of cells,reduce side effects and enhance the stability of electrolyte.