Electrode kinetics of oxygen reduction on oxide-free platinum electrodes

Abstract

The cathodic V log i curves for O2 reduction on oxide-free Pt electrodes were determined in oxygen-saturated purified acid (HClO4, pH 1–3) and alkaline (NaOH, pH 13) solutions. It was found that ∂V/∂ log i = −2·3RT/F, ∂V/∂ log pO2 = −2·3RT/F and ∂V/∂ pH = −100 mV. Coverage of electrodes by oxygen-containing species was determined by superimposing a constant cathodic current over the working electrode. Intermediate values of coverages were found to be nearly linearly dependent on the potential in the Tafel region.The kinetics mechanism of O2 reduction on oxide-free Pt electrode are different from that reported for the oxide-covered electrode. Reaction mechanism are discussed in terms of Langmuir and Temkin adsorption isotherms. It is suggested that under Temkin conditions the rate-determining step in the over-all four-electron process is the first electron transfer.