Modification Of Electrode Materials And Optimization Of Flow Velocity In Vanadium Redox Flow Battery

The all-vanadium redox flow battery(VRFB)is a new type of energy storage battery,which is very suitable for medium and large-scale stationary application.Because the active materials in the positive and negative electrode electrolytes are all vanadium ions,it not only has the advantages of traditional flow battery,such as,flexible capacity and power,long cycle life,high safety and no pollution,but also effectively avoids crosscontamination during charge-discharge.The performance of VRFB is mainly restricted by three key materials: electrolyte,ion exchange membrane and electrode.For the electrolyte,we should improve the system to increase its stability;for the ion exchange membrane we should reduce the penetration of vanadium ions and water;for the electrode we should improve the conductivity and electrochemical catalytic activity.These measures will greatly increase the efficiency and cycle life of VRFB,which are beneficial to its application in actual production.In this paper,the modification of the graphite felt electrode for VRFB is studied first.The microparticles of manganese dioxide are deposited on the surface of graphite felt carbon fiber.In order to enhance the adhesion of these particles with carbon fibers,manganese dioxide-modified graphite felts were heat-treated at high temperatures in an argon atmosphere to obtain manganese oxide-modified graphite felt electrodes,and the modified electrodes were subjected to various characterizations.The study shows that the graphite felt electrode modified by manganese oxide can grow an irregular product particle on the surface of carbon fiber,change the surface morphology of the material,and improve the wettability of the graphite felt electrode.In addition,the modified graphite felt electrode improves the catalytic performance of the V(IV)/V(V)electrocatalytic reaction and reduces the polarization of the electrode.The chargedischarge test results show that the modified graphite felt electrode can indeed improve the voltage efficiency and energy efficiency of the battery while maintaining good stability over a long period of time.Then a transient model of a simple two-dimensional all-vanadium redox flow battery was constructed.The reasons for capacity decay in VRFB were simulated using Comsol software.That is,the vanadium ions in the positive and negative electrolytes penetrate the ion exchange membrane and cause amount of vanadium ions unbalanced.Based on this model,the electrolyte flow rate was changed and the influence of the flow rate on the capacity decay was obtained.The results demonstrate that the change of the electrolyte flow rate will lead to the uneven distribution of vanadium and hydrogen ions in the porous electrode of the battery,resulting the penetration of vanadium ions in ion exchange membranes of different valence states,and affecting the capacity degradation of the battery.According to the research results,the flow rate of the electrolyte should be increased as much as possible to reduce the rate of battery capacity decay and increase the cycle life of the battery.