Temperature-related reaction kinetics of the vanadium(iv)/(v) redox couple in acidic solutions

Abstract

The temperature-related reaction kinetics of the VO₂⁺/VO²⁺ redox couple on a graphite electrode in sulfuric acid solutions has been investigated by cyclic voltammetry and chronopotentiometry for a better understanding of positive half-cell in a practical vanadium redox flow battery (VRFB). Elevated temperature facilitates the VO₂⁺/VO²⁺ redox reaction but without significant effect on its reversibility, and the reaction rate constants are calculated to be in the order of 10⁻³ cm s⁻¹. In addition, the diffusion coefficient of both VO²⁺ and VO₂⁺ ions tends to increase with increasing temperature with a diffusion activation energy of 4.24 kJ mol⁻¹ for VO²⁺ and 25.2 kJ mol⁻¹ for VO₂⁺. On this basis, two diffusion equations for both VO²⁺ and VO₂⁺ ions in sulfuric acid solutions have been established.