Dissociative adsorption of thiourea at a polycrystalline silver electrode in alkaline media

In alkaline solutions, when the potential of the silver electrode is more than -450 mV vs sce, thiourea undergoes decomposition and a sparingly soluble silver sulfide film forms as a product of the accompanying anodic reaction. These processes are controlled by convective diffusion and depend upon the thiourea concentration. During the reverse cathodic scan, two cathodic stripping peaks are observed. The first one corresponds to the stripping of Ag₂S (bulk) and the second one to the stripping of an adsorbed layer of Ag₂S. Hydrosulfide ion (HS^-) are produced by these two cathodic reactions. The formation of an adsorbed layer of Ag₂S has been confirmed in rotating ring-disk electrode experiments.