Electrochemical studies of oxide-free nickel surfaces
Date
1990
Authors
Hennig, Darren Lewis
Journal Title
Journal ISSN
Volume Title
Publisher
Abstract
The initial stages of oxidation of nickel surfaces in aqueous alkaline solutions and in acetonitrile with trace amounts of water were studied by cyclic voltammetry. To verify that the initial metal surface was free of oxide , a surface preparation method was developed , in which a chemical polishing solution was exchanged in-situ by the working solution , while maintaining potential control and oxygen-free conditions. In this way oxide formation from trace atmospheric oxygen or from inadvertent positive potential excursions was avoided. The results using this method on polycrystalline electrodes were compared to those on surfaces prepared by less rigorous electropolishing methods used by other workers . In addition, a single-crystal Ni(111) electrode was prepared, and its behavior was compared to that of the polycrystalline electrodes.
Significant differences in the cyclic voltammetry peak shapes and in the oxidation/reduction charge ratios were found for the different surface preparations, particularly in the case of the peak for initial oxidation to a-(nickel hydroxide). The results are interpreted in terms of the defect densities of the oxide films , and it is concluded that the films increased in defect density in the order: Ni(111) prepared by the solution exchange method, and polycrystalline Ni prepared with electropolishing. The single crystal surface was found to be about 50% more reactive than the corresponding polycrystalline surface, and this was attributed to favorable epitaxy on the (111) face.