Kinetic studies of dioxygen and superoxide ion in acetonitrile at gold electrodes using ultrafast cyclic voltammetry

On the basis of a circuit with ohmic drop compensation by electronic positive feedback, ultrafast cyclic voltammetry was used to study the electrochemical behavior of dioxygen and superoxide ion at gold electrodes in acetonitrile containing 0.9 M tetraethylammonium tetrafluoroborate as the supporting electrolyte. At low scan rates, the O2/O2- couple is controlled by diffusion, and its redox process is an irreversible one with the rate constant (7.38 ± 1.25) × 10−3 cm s−1. The diffusion coefficient of O2 in such a solution was deduced as (4.87 ± 0.08) × 10−5 cm2 s−1, while at high scan rates, it is controlled by the adsorbed O2 at a rate constant (5.21 ± 0.66) × 104 s−1. At moderate scan rates, it is controlled by both of them simultaneously. As to the O2-/O22- couple, its faradaic signal was greatly distorted at low scan rates. However, when the scan rate was increased sufficiently, the perturbing reactions would be 'out-run' by a transient experiment. Then, kinetic information could be obtained from the well-shaped voltammograms. In our experiments, the adsorption of O2- was found, and the rate constant was deduced as (1.95 ± 0.28) × 104 s−1.