The Electrode Kinetics of Oxygen Reduction: A Case Study. The Corrosion of Copper and its Alloys in Aqueous Chloride Solution at a Smooth Rotating Disk Electrode

Abstract

The importance of oxygen reduction in corrosion processes is emphasized. The complex mechanism of this electrode process, due to 2- or 4-electron pathways, surface adsorption, and surface oxide formation resulting in possible passivity, is highlighted. Oxygen reduction can be controlled by charge (electron) transfer, mass transport of dissolved oxygen to the electrode surface, or both (mixed control). In practice, mixed control is common. Quantitative studies of the electrode kinetics of oxygen reduction at copper and its alloys and its simulation are illustrated by the use of a rotating disk electrode in aqueous chloride electrolytes at a temperature of 25°C. A variety of techniques is used to calculate the corrosion current density. The diffusion coefficient of dissolved oxygen if estimated via the Levich equation (under complete mass transfer control) and the Koutecky–Levich equation (under mixed control) is 1.9±0.2×10−5cm2s−1 at 25°C. Other important cases of oxygen reduction in electrochemical technology are indicated, including gas and dissolved oxygen sensors, the negative electrode of metal-air batteries and fuel cell cathode reactions. Areas deserving further research and development are identified while broader subject areas include diverse bifunctional oxygen electrocatalysts for reversible batteries and regenerative fuel cells.