VRB Transfer Test Of Vanadium Ions Across Nafion117 And Microscopic Analysis Of The Electron Conductivity Of Electrode

Vanadium Redox Flow Battery(VRB)is a large-scale energy storage battery.VRB has the advantages of longer service life,higher energy efficiency,lower cost,non-pollution protection,and independence between energy storage capacity and output power.So it has played an important role in new large-scale energy storage technologies.It has been used in renewable energy generation,remote power supply and other fields.At present,it has carried out demonstration projects in many countries and regions such as China and America,and has broad application prospects.However,VRB has the problem of self-discharge caused by transmembrane transport of vanadium ions,which is one of the factors limiting the application of VRB.Meanwhile,the lack of theoretical research on electrode materials has also limited the development of VRB.Therefore,in-depth study of vanadium ion transmembrane transfer mechanism and electrode material properties in VRB is of great significance for the improvement of VRB performance and the promotion of VRB in the field of energy storage.Based on a large number of literatures on VRB,this thesis summarizes the research status and application status of VRB,and explains the working principle,electrochemical principle,structure and characteristics of VRB.Meanwhile,the transport behavior of vanadium ions in Nafion 117 at different temperatures and concentrations and the micro-simulation of the electronic conductivity of electrodes were emphatically studied.In the transfer test of vanadium ions across Nafion117 membrane,the transfer of four valence vanadium ions in the proton exchange membrane was tested by a self-designed test device.The absorbance of four valence vanadium ion solutions was tested using TU-1900 dual beam ultraviolet visible spectrophotometer.The relationship between the four valence vanadium ion concentrations and absorbance was obtained by fitting method.Finally,the diffusion coefficient of vanadium ion in proton exchange membrane was calculated and analyzed.The effect of temperature and concentration on the transmembrane transport of vanadium ion was further analyzed to study the self-discharge problem of VRB.Results showed the diffusion coefficient of vanadium ion in proton exchange membrane is lower than that of water in proton exchange membrane.The diffusion coefficient of vanadium ion in Nafion 117 film can be reduced by increasing the concentration of vanadium ion solution and decreasing the temperature of vanadium battery.In the simulation calculation of electrode materials,the first-principles pseudopotential plane wave method based on density functional theory was used to study the effect of oxygen-containing functional groups on the electron conductivity of electrodes.The calculation models of graphite felt and graphene oxide electrodes for VRB were established.The density of states,atomic orbital charge distribution and energy analysis of the electrodes containing different oxygen functional groups were carried out respectively.Results of simulation analysis showed that after oxygen atoms and hydroxyl groups are adsorbed on the surface of graphite felt electrode,electron transmission ability increases.After adsorption of carboxyl groups,the locality is enhanced,the formation energy is the smallest,and the system is the most stable.Compared with C=O double bond graphene oxide,C-O single bond graphene oxide has better electron transport ability.When the hydroxyl group is adsorbed,the density of the graphene electrode is more gradual than that of the graphite felt electrode,and the delocalization is stronger,and the electron conductivity is better.