Arrhenius Variation of Precipitation Time for V-V in Vanadium Flow Batteries

Both visual observation and light-scattering measurements were used to investigate the stability of typical vanadium flow battery (VFB) catholytes. V2O5 precipitates after an induction time that decreases with increasing temperature and concentration of Vv and increases with concentration of sulphate. This was observed at 30- 60°C for Vv and sulphate concentrations of 1.4-2.11 and 3.7-5.3 mol dm"3, respectively. Arrhenius plots of induction time show excellent linearity and the logarithm of induction time varies linearly with both sulphate and Vv concentration. An Arrhenius plot of induction times normalized to standard reference concentrations of sulphate and Vv for all solutions gave a good straight line. The activation energy estimated from the slope is E# = 1.79 eV. Combining the Arrhenius Equation and the observed variation with sulphate and Vv concentrations, an equation was derived which enables us to simulate the induction time for any catholyte solution at any temperature in the range investigated.