Investigation of the interaction between cobalt sulfide coatings and Ag(I) ions using cyclic voltammetry in KClO4 and NaOH aqueous solutions and X-ray photoelectron spectroscopy

Cobalt sulfide coatings have been investigated by means of cyclic voltammetry in 0.1 M KClO4 and 0.1 M NaOH solutions and analyzed using X-ray photoelectron spectroscopy. They have been shown to contain CoS(OH), COS and Co(OH)(2). After treating such Co sulfide coatings with AgNO3 Solution, their composition changes: both the cobalt and oxygen content decreases and Ag (up to 85 at%) appears in the coating as Ag2S, Ag2O and metallic Ag. Co(II) compounds react with Ag+ ions according to an exchange reaction [COS + 2Ag(+) + 2H(2)O --> Ag2S + Co(OH)(2) + 2H(+)]. In the course of the reaction Of Co(OH)(2) with silver ions, a redox process occurs, giving metallic silver [Co(OH)(2) + Ag + + H2O --> Ag-o + CO(OH)(3) + H+ or Co(OH)(2) + Ag+ --> Ag-o + CoO(OH)+H+]. Ag2S reduction takes place at more positive potentials than Cu reduction; therefore sulfide layers of cobalt modified with silver ions, unlike unmodified ones, may be plated with Cu from both acid and alkaline electrolytes.