Studies on Electrode Processes of Oxovanadium(IV). I. Polarographic Behaviors and Photochemical Reaction in Potassium Oxalate Solution

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Oxovanadium(IV) was found to develop a fairly stable oxidation wave as well as a reduction wave at the dropping mercury electrode in an aqueous solution containing M potassium oxalate. The predominant entity in the solution was [VO(ox)2]2− , and both the oxidation wave with one-electron transfer, and the reduction wave with two-electron transfer were irreversible. The anodic transfer coefficient evaluated from the logarithmic plot and Tafel plot was 0.60–0.63, and the exchange current density estimated tentatively from the Tafel plot was 1.8×10−6 A/cm2. The effect of aerial oxidation of V(IV) to V(V) and the photochemical reduction of V(V) to V(IV) were investigated through the controlled potential electrolysis, absorption spectroscopy and ESR studies. The polarographic kinetic current of the oxidation process was observed under ultra-violet light irradiation. The apparent rate constant of the photochemical reduction evaluated from the kinetic current was (0.02–0.04)/εφI0s−1, where ε is the molecular extinction coefficient, φ the quantum yield and I0 the intensity of the incident light.
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