Electrochemistry of the HO2 and O –2 radicals under steady state conditions. Part 1.—The electrochemistry of O –2 at neutral pH

Abstract

The electrochemistry of the O₂^– and HO₂ radicals on platinum, gold and mercury electrodes has been studied at neutral pH. The electrochemical kinetics have been elucidated by studying the effect of [O₂^–], [O₂], [H₂O₂] and [H₂] on the rest potentials and the polarization resistances of the electrodes. The polarization resistance is linearly related to [O₂^–] and is independent of [O₂], [H₂O₂] and [H₂], while the steady potential is nearly independent of [O₂^–], [O₂], [H₂O₂] and [H₂], but rises with increasing catalytic activity of the electrode. It is shown from these and other data that, at neutral pH, the steady potential is a mixed potential with the component reactions O₂+ e^–⇌ O^–₂ and probably O^–₂+ 2H⁺+e^–⇌ H₂O₂.

The potential on platinum, gold and mercury electrodes at pH 7 lies between 0.24 and 0.42 V (vs. n.h.e.). The more catalytically active the electrode the more positive the potential. The component reactions under acid and alkaline conditions are different and are discussed in the following paper. In all cases, the net effect is the disproportionation of the radicals to O₂ and H₂O₂ by pairs of one electron redox processes. Aspects of the mixed potential theory have been tested in detail.