Studies On Physicochemical Properties Of Positive Electrolyte Of Vanadium Redox Flow Battery

The electrolyte solution of the all-vanadium redox flow battery(VRFB)is one of the most critical components for its function on energy-bearing and conversion.However,the electrolyte of VRFB is characterized by high concentration and complicated components.Meanwhile,during the operation,the physicochemical properties of the electrolyte could change with the working states,which will in addition directly affect the overall cell performance and behavior.Therefore,it has the vital significance to probe into the physicochemical properties and change law of the electrolyte in VRFB.In this dissertation,conductivity,surface tension,viscosity and density for electrolyte of VOSO4+H2O,VOSO4+H2SO4+H2O and VOSO4+HC1+H2O systems in VRFB were investigated and their variations with temperature and components were discussed.From the calculated physical chemistry properties and thermodynamic parameters,the micro internal interactions such as the salvation and association state were obtained.Moreover,semi-empirical equations to predict solution properties were proposed.Meanwhile an online SOC monitoring approach for redox flow battery based on density and viscosity was proposed.In addition,this study will benefit providing basic data and theory for the application of VRPB and intensify the knowledge of the influence mechanism for the electrolyte to the battery performance.Furthermore,the study can enrich and develop the theory of electrolyte solution in general and acquires the following major results:(1)The molar conductance,limiting molar conductance,dissociation constant of ion-pair[VOSO4]0 and thermodynamic functions for the dissociation process were determined.The analysis of the related mechanism indicates that the reaction of ion-pair dissociation can't occur spontaneously while the dissociation entropy is the resistance of the dissociation process.(2)A new definition of molar surface Gibbs free energy was proposed and used to predict the surface tension of the aqueous VOSO4.Based on this new concept,an improving Eotvos equation in which each term has a more explicit physical meaning was subsequently presented.Furthermore,the molar surface enthalpy,entropy and other thermodynamic functions derived from the improving equation were evaluated.(3)The mean apparent molar volume and limiting partial molar volume of VOSO4+HC1+H2O were calculated.It shows that VOSO4 can interact with aqueous HCl and the interaction decreases with the HC1 concentration increasing.Meanwhile,a method to obtain the density of a binary system by extrapolation from the ternary system was proposed.(4)The activation energy of viscous flow,viscosity coefficients B,activation parameters for viscous flow of the solution and other thermodynamics parameters of aqueous VOSO4 were evaluated.The results indicate VOSO4 and V02+ are structure makers that have structure-making effect on water.The viscosity of the ternary system of VOSO4+H2SO4+H2O is higher than VOSO4+HCl+H2O,which shows the interaction between VOSO4 and H2SO4 is stronger.Based on Eyring equation,a semi-empirical predicting equation to estimate the viscosity for concentrated and mixed-solvent electrolyte solutions with a good result was put forward.(5)An empirical neural network model that correlates the SOC to electrolyte viscosity and temperature was established.Benefit from the Darcy's law,an online SOC monitoring approach for redox flow battery was proposed.