Multicycle chronoamperometry at rotating ring-disc electrode as a method of current separation into partial currents of silver ionization, Ag₂O formation and its chemical dissolution in alkaline medium

Abstract

A method of multicycle chronoamperometry at rotating ring-disc electrode is suggested for experimental separation of the disc polarization current into its components that correspond to the substrate metal ionization, an oxide formation, and the oxide chemical dissolution. The method was validated by the example of the Ag|Ag₂O|OH⁻(H₂O) system. At moderate anodic potentials of Ag-disc (0.48–0.51 V), silver active dissolution from open areas of its surface and through film’s pores dominates; the phase-forming current, hence, the current efficiency of this process drops down rapidly. At the potentials of the maximum at voltammograms (0.52–0.53 V), when the silver active dissolution current is suppressed, the phase-forming currents dominate; they exceed the oxide chemical dissolution rate significantly. The Ag₂O film thickness increases rapidly, the current efficiency of the oxide formation process approaches 100% during the entire disc polarization period. The Ag(I)-oxide chemical dissolution rate constant practically does not depend on the anodic phase-formation potential; however, it somewhat varies depending on the oxide film thickness, thus reflecting changes in the film structure and, possibly, chemical composition (from AgOH to Ag₂O).