Analysis Of Mass Transfer Characteristics Of Electrode For All Vanadium Flow Battery

All-Vanadium redox flow battery(VRFB or VRB)is an innovative large scale energy storage battery combining lots of advantages,such as long service life,high efficiency and environmental protection.The VRB is widely used in many fields for its unique storing energy,which can convert wind energy,solar energy,hydrogen energy directly into electricity through electrochemical processes.In numerous factors,the characteristic of electrode has a tremendous effect on VRB performance.Water as the main composition of vanadium battery electrolyte,its distribution in the electrode of vanadium battery performance also has a great influence.In this thesis,a large amount of referenced literature data is used to introduce the development history and research status of VRB,summarize the structure and function of VRB,expound reaction principle of the electrode and the research process of key components.The theories of electrochemical thermodynamics and kinetics of the electrode process were introduced in this thesis.The VRB test platform is set,including the charger,piping system,electronic load,the electrolyte storage tank,micro flow pump,battery monitoring system,computer management system and software system.The VRB fabricated,including flow field plate,graphite felt diffusion layer,proton exchange membrane,current collection board,plywood,etc.The procedures and matters needing attention were obtainted by test the platform.In this thesis,electrode electrochemical activity was improved through concentrated sulfuric acid oxidation treatment.Then,the modified electrode was tested by electrochemical method,including volt-ampere characteristic,ac impedance,and physical means,including scanning electron microscope in order to obtain the parameters of vanadium battery best performance.The results show that,concentrated sulfuric acid oxidation treatmen can improve the performance of vanadium battery;Vanadium battery performance will not always increased with the increase of concentrated sulfuric acid oxidation time;the influence of concentrated sulfuric acid is Faraday impedance of the positive and negative of battery.Based on the principle of Martini force field,the coarse graining model of water and electrodes were constructed by Materials Studio software,and the influence of the temperature,the mass fraction of the capillary,and the length of the capillary on the water self-diffusion behavior was analyzed in the graphite felt electrode by mesoscopic dynamics simulation.The relationship between different factors and water self-diffusion coefficient was investigated by analyzing the mean square displacement,and the influence of different factors on the ordering of water in the model was analyzed by employing the radial distribution function.With the increase of temperature,water self-diffusion coefficient in the electrode increased,and the ordering decreased.With the capillary length increased,the self-diffusion coefficient of water in the electrode was reduced,the ordering remained unchanged.With the mass fraction of the capillary increased,the capillary for water self-diffusion behavior in the graphite increased,and reduced the ordering of water in electrode.The simulation results were compared with the experimental data,and showed the same tendency and magnitude,proved the reliability of the model.