Anodic behavior of cobalt silicides in potassium hydroxide solutions

Anodic behavior of a CoSi2 electrode in 0.1-4 M KOH solutions and a Co2Si electrode in 1 M KOH was studied in a range from the corrosion potential (E (cor)) to the oxygen evolution potentials with the use of polarization and impedance measurements. A number of results indicate enrichment of electrode surface layers in cobalt. At potentials from E (cor) to E (tp) transpassivation potential, impedance spectra correspond to the passive state of the silicides. At potentials from E (tp) to the onset potential of oxygen evolution, impedance spectra can be described taking into account the inclusion of hydroxide ions in the passivating film. Equivalent electric circuits are proposed for different electrode potential ranges.