Solubility Rules of Negative Electrolyte V₂ (SO₄)₃ of Vanadium Redox Flow Battery

The solubility of V(III) species in negative electrolyte of all vanadium redox flow battery (VRB) was studied and the solubility parameters of V(III) species at various concentrations of H2SO4 and different temperatures were preliminarily obtained. The results showed that dissolution of V(III) was an exothermic process. The solubility of V(III) decreased with temperature (15−40°C). Also, the presence of V(III) in the solution was a V−O−V dimmer. The solubility of V(III) decreased with the increasing of H2SO4 and low concentration of H2SO4 would keep high concentration of V(III) stable for a long time. Especially, concentration of V(III) could reach 2.730 mol/L with 1 mol/L H2SO4 at 30°C . Electrochemical properties was further investigated by experiment, the results revealed that V(III)-H2SO4 solution was an irreversible system for V(III)/V(II) redox reaction. Increasing of concentration of H2SO4 had great benefit to improve the reversibility of V(III)/V(II) redox reaction.