Measurement and accurate prediction of surface tension for VOSO4-H2SO4-H2O ternary electrolyte system at high-concentration in vanadium redox flow batteries

Abstract

Surface tension is an important thermodynamic parameter for vanadium redox flow battery (VRFB) however its related theoretical study for multicomponent systems containing sulfuric acid at high concentration is rare due to the complexity of ion interaction in the electrolyte. In this work, the surface tension and density of VOSO4-H2SO4-H2O electrolyte solution were firstly measured at different temperatures from 283.15 to 313.15 K over a wide range of solute concentration. The average molar volume (V) was calculated according to above experimental data, and then the new definition of molar surface Gibbs free energy (gs) and improved Eötvös equation for VOSO4-H2SO4-H2O ternary solution has been derived based on Li’s theory. Simultaneously, several thermodynamic data of this ternary solution were obtained, such as the value of molar surface entropy, s, molar surface enthalpy, h, and Eötvös empirical parameter. In addition, the high-accuracy and semi-empirical equation was established to predict the surface tension of the VOSO4-H2SO4-H2O ternary solution based on the new gs definition. The results revealed that predicted values are in good agreement with the experimental values and correlation coefficient is 0.9993. This work provides basic data for mass transfer and heat transfer analysis of the VRFB and it also provides convenience for evaluating the interface effect between the electrolyte and other components when optimizing the composition of electrolyte and improving battery performance.