Study On Thermodynamic Properties Of Electrolyte For All Vanadium Redox Flow Battery

The vanadium redox flow battery (VRB) is a new electrochemical energy storage system, which can store the energy transformed from unstable sources of energy such as wind and solar due to its advantages such as large current density for charge and discharge, low self-discharge and simple construction. The cell employs the VO2+/VO2+and V2+/V3+redox couples in the positive and negative half-cell electrolytes, respectively, with sulfuric acid as the supporting electrolyte. It is not only the conducting medium, but also the energy-storage medium in battery. Vanadium electrolyte is the core of energy storage and energy conversion of VRB. However, only a few researches focus on influence of pH on electrolyte concentration of vanadium and there is no explanation. Therefore, the author wants to explain the low for the thermodynamic stability of vanadium ions in electrolyte of VRB.This paper has finished the three aspects of the research on electrolyte of vanadium redox flow battery.1. According to literature, E-pH figure for vanadium ions exist is painted. The influence of the concentration of vanadium ions, pH, and the concentration of H2SO4on stability of vanadium ions is investigated and the change low is also obtained.2. The permeability coefficient, Pitzer parameters and activity coefficients in VOSO4-H2O system is investigated by using equal-pressure method. The permeability coefficient of water linearly increases as VOSO4concentration increasing in VOSO4-H2O system, which indicates higher free transfer ability. According to Pitzer parameters, the hydration form of VOSO4being existed in electrolyte is conformed, and indicates a stereochemical structure of VOSO4. The activity coefficient of VOSO4increases with the increasing concentration of VOSO4.3. Cyclic voltammetry, polarization curve and impedance test method are used to study the effects of Fe and impurities Si on stability of vanadium battery electrolyte at298.15K. When the content of Si is no more than0.01mol/L, there is not obvious change. When the content of Fe impurity is no more than0.01mol/L, there is a slight improve electrochemical properties of1.0VOSO4+3.0mol/L of electrolyte. When the impurity content of Fe reaches0.001mol/L the beneficial reaches biggest. Therefore, for electrolyte preparation, the content impurities of Si and Fe should be controlled lower than0.01mol/L and0.001mol/L respectively.