The electrochemistry of silver in sulphide and tetrasulphide solutions

Abstract

A cyclic voltammetric and rotating disc study of the sulphide and tetrasulphide ions on glassy carbon and silver electrodes is described. Oxidation of the tetrasulphide ion on glassy carbon produces a thin film of sulphur. In the case of the sulphide or hydrosulphide ion on silver, two sets of peaks were observed. The set with the more negative potential was shown to be due to the electrochemical formation and decomposition of α- and β-silver sulphide (Ag 2S). The silver sulphide formation was limited by diffusion of HS − in solution, the diffusion coefficient being (11.9 ± 0.5) × 10 −10 m 2 s −1. The more anodic set of peaks was shown to be due to the silver dissolution reaction, followed by the chemical precipitation of silver sulphide. The tetrasulphide ion—silver system showed similar behaviour, but with two additional features. One was an extra silver sulphidation peak which was ascribed to the direct electrochemical reaction between silver and the tetrasulphide ion. The other was the reduction of the tetrasulphide ion to sulphide at large negative potentials. Under rotation, a diffusion plateau for this reaction was observed, from which a diffusion coefficient for S 4 2− of (5.9 ± 0.2) × 10 −10 m 2 s −1 was determined.