A faradaic impedance study of the reduction of oxygen from aqueous alkaline solution at the dropping mercury electrode

Abstract

The reduction of oxygen to hydrogen peroxide at a dropping mercury electrode in an aqueous solution of 1 M KNO3+0.04 M KOH (pH=12.35) has been studied by means of impedance measurements as a function of frequency and d.c. potential. The reaction appears to be nearly reversible in the dc sense, but quasi-reversible in the ac sense. The impedance data obey the Randles' equivalent circuit with the following apparent values for the kinetic parameters: standard heterogeneous rate constant ksha=0.035 cm s−1 and cathodic transfer coefficient αac=0.22. The results are interpreted in terms of a two-step charge transfer mechanism with the step O2+eO2− being rate-determining.