Study of the Kinetics of Vanadium (II)/(III) Redox Reaction

Vanadium redox flow battery (VRB) is a novel electrical energy storage system. The cell voltage loss is mainly due to the sluggish reaction of these redox reactions, it also affects the overall VRB energy storage efficiency. Rotating disk electrode (RDE) was used to measure the polarization curves of V(IV)/(V) and V(II)/V(III) redox reactions in different electrolyte compositions. On Carbon electrode, the rate constants of V(IV) oxidation is much slower than the rate constant of V(II) oxidation. The mainly voltage loss is due to the V(IV)/(V) in the electrolytes on positive electrode. We also found that the Stoke radius of V(IV)/V(V) ion is larger than the Stoke radius of V(II)/V(III). This provides a reasoning of lower reaction constant of V(IV)/V(V) ion pair.