Effects of Temperature and Composition on Catholyte Stability in Vanadium Flow Batteries: Measurement and Modeling

Abstract

The stability of typical V flow battery (VFB) catholytes was studied at temps. in the range 30-60° for VV concns. of 1.4-2.2 mol dm-3 and sulfate concns. of 3.6-5.4 mol dm-3. In all cases, V2O5 ppts. after an induction time, which decreases with increasing temp. Plots of the logarithm of induction time vs. the inverse of temp. (equiv. to Arrhenius plots) show excellent linearity and all have similar slopes. The logarithm of induction time also increases linearly with sulfate concn. and decreases linearly with VV concn. The slopes of these plots give values of concn. coeffs. βS and βV5 which were used to normalize induction times to ref. concns. of sulfate and VV. An Arrhenius plot of the normalized induction times gives a good straight line, the slope of which yields a value of 1.791 ± 0.020 eV for the activation energy. Combining the Arrhenius equation with the obsd. variation with sulfate and VV concns., an equation was derived for the induction time for any catholyte at any temp. in the range studied. Although the mechanism of pptn. of VV from catholytes is not yet well understood, a precise activation energy can now be assigned to the induction process. [on SciFinder(R)]