Performance Test Of All Vanadium Flow Battery And Mesoscropic Mass Transfer In Its Membrane

All Vanadium Flow Battery(VRB)is a kind of high efficiency and clean energy storage system,with the advantages of large capacity,high power,long life cycle and so on,which is more apply to large-scale energy storage.In recent years,VRB has been rapidly developing and has been demonstratively used in America,Japan,China and Canada,which is mainly used in power stations such as wind power,solar energy,etc.However,due to its disadvantages such as small temperature range and low energy-density,it has limited the application range of all vanadium flow battery,which has limited its development.In this thesis,according to the thermodynamic theory and the electrode process kinetics theory foundation of the vanadium flow batteries,the VRB testing platform was built and debugged.The key research was the influence of membrane thickness on characteristics and membrane mesoscopic mass transfer for all vanadium flow battery.The designed battery flow field plate,collector plate,electrode frame,graphite felt electrode and proton exchange membrane were assembled into the all vanadium flow battery cell,and tested the influence of proton exchange membrane,electrolyte concentration and current density on the characteristics of VRB charge and discharge,AC impedance,coulomb efficiency,voltage efficiency and energy efficiency.According to the equivalent circuit method,the all vanadium flow battery equivalent circuit was found,and analyzed the effects of proton exchange membrane thickness on Ohm impedance,positive Faraday impedance and negative Faraday impedance.The results showed that,increasing the proton exchange membrane thickness,the charging and discharging time can be prolong,and the AC impedance diagram was shifted to the right,but the efficiency reduced.The equivalent circuit of all vanadium flow battery was composed of Ohm impedance,positive Faraday impedance,negative Faraday impedance and positive and negative capacitance.Reducing the thickness of the proton exchange membrane can decrease the battery ohm impedance and improves the performance.For mass transmission plays a crucial role in all vanadium flow battery,in order to analyze the transfer mechanism of water and hydronium ion in proton exchange membrane,in this thesis,according to the Dissipative Particle Dynamics(DPD),Materials Studio software was used to build the coarse-grained model of Nafion117,water and hydronium ion,which corresponded with the Newton’s law.Based on the theory of dissipation particle dynamics,the three-dimensional topology of water channel in Nafion membrane was analyzed and the influence of temperature,water and hydronium ions contents and the number of water molecules on the diffusion coefficient and radial distribution function of water and hydrated hydrogen ions in Nafion membrane were analyzed.The distribution of water and hydronium ions around sulfonic acid group and the effects of water and hydronium ions contents on coordination number was analyzed by radial distribution function.The study showed that,with the increase of water and hydronium ions contents,the water cluster in Nafion membrane can gradually formed interconnected and cavernous continuous water channel,which promoted the water and hydronium ion transfer,and make the diffusion coefficient increased.The results of the study provide a reference for improving the liquid phase mass transfer of all vanadium flow battery.