Effect of Pretreatment on the Rate of the VO²⁺/VO₂ ⁺ and V²⁺/V³⁺ Reactions at a Carbon Electrode

Abstract

It was shown by cyclic voltammetry, current measurements at constant potential and electrochemical impedance spectroscopy that polarization pretreatment of glassy carbon electrodes affects the kinetics of the VO 2+ /VO 2 + and V 2+ /V 3+ redox reactions. After pretreatment at potentials more positive than ~0.7 V (sat. Hg/Hg 2 SO 4 ), electrodes were less active both for oxidation of VO 2+ and for reduction of VO 2 + . The activity of the electrode remained depressed indefinitely but was recovered by pretreatment at negative potentials. However, the converse was observed for the V 2+ /V 3+ redox reactions: after pretreatment at positive potentials electrodes were more active for oxidation of V 2+ and reduction of V 3+ than after pretreatment at negative potentials. Both activation and deactivation (for VO 2+ /VO 2 + ) occurred relatively quickly, typically within ~60 s. and eventually approached a steady state characteristic of the particular pretreatment potential. It is suggested that oxygen species formed on the electrode during anodization inhibit the VO 2+ /VO 2 + electrode reaction but enhance the V 2+ /V 3+ electrode reaction.