Electrocatalytic activity of cobaloxime complexes adsorbed on glassy carbon electrodes toward the reduction of dioxygen

We report here a detailed study concerning the electrochemical behavior of two cobaloxime complexes adsorbed on glassy carbon electrodes and their applications to electrocatalytic activity for dioxygen reduction. The complexes were adsorbed irreversibly and strongly on the surface of preanodized glassy carbon electrodes. The electrochemical behavior and stability of the modified electrodes as well as the two-electron reduction of O2 at the electrodes were investigated using cyclic voltammetry, chronoamperometry and rotating disk electrode methods. At the modified electrodes, the reduction of dioxygen to hydrogen peroxide occurs at potentials where it is not observed at a bare glassy carbon electrode. The modified electrodes exhibited potent and persistent electrocatalysis for O2 reduction in acetate buffer solutions of pH 4.0 with the domination of an overpotential of about 950 mV and an increase in the peak current. The heterogeneous rate constants for the reduction of O2 at the surface of modified electrodes were determined by rotating disk electrode voltammetry using the Koutecký–Levich plots. A possible catalytic mechanism is proposed and discussed.