Measurements of V^V Precipitation Times and Simulation of the Stability of Catholytes in Vanadium Flow Batteries

The stability of vanadium flow battery (VFB) catholytes was investigated using both lightscattering measurements and visual observation. V2O5 precipitates after an induction time τ which shows an Arrhenius variation with temperature. The value of τ increases with increasing concentration of sulfate and with decreasing concentration of V^V but the activation energy remains constant with a value of (1.791±0.020) eV. Plots of ln τ against [S] and [V^V] show good linearity and the slopes give values of β_S = 2.073 M^-1 and β_V5 = -3.434 M^-1 for the fractional rates of variation of τ with [S] and [V^V], respectively. Combining the Arrhenius Equation with the observed log-linear variation of τ with [S] and [V^V] provides a model for simulating the stability of catholytes.