Potential–pH diagram for sulfur and hydroxyl adsorbed on silver in water containing sulfides

An equilibrium potential–pH (Pourbaix) diagram is presented for sulfur adsorbed on Ag(1 1 1). It allows prediction of the E–pH conditions of adsorption of sulfur and hydroxyl on silver surfaces immersed in water containing dissolved sulfur species such as sulfides. The E–pH relations associated with the equilibria between water and adsorbed hydroxyl, and between dissolved sulfur species and adsorbed sulfur are given at 25 °C. The E–pH adsorption diagram is calculated for a sulfur concentration of 10−3 mol kg−1 and superimposed to the usual Pourbaix diagram for the SAgH2O system. It is shown that an adsorbed sulfur monolayer may form on the silver surface in E–pH domains in which usual Pourbaix diagrams predict no stability of the bulk silver sulfide Ag2S. The calculation of stability domains of adsorbed hydroxyl and sulfur allows prediction of the electrocatalytic and corrosion behavior of Ag in water with sulfur species.