Surface structural changes of evaporated thin silver film electrodes during the adsorption of chloride ion

Abstract

It is well known that the surface of metal electrodes undergoes structural changes when subjected to different electrochemical treatments (potential cycling, upd reactions, etc) [l-5]. The structural changes of silver in certain electrolytes. particularly chloride. have received much attention because of their connection with the appearance of the SERS effect. The capacitance vs. potential curve of single silver crystals in chloride solutions [6] exhibits a narrow peak in the potential range between -0.5 and 0.0 V (vs. SCE), depending on the crystallographic orientation. Apparently this peak does not appear in polycrystalline silver and evaporated silver thin films [7-91. The peak has been attributed to partial charge transfer and later to a rearrangement of the adsorbed surface layer by Valette et al. [6,10] and to a reconstruction of the silver surface layer by Fleishmann et al. [ll]. Voltammetric studies with polycrystalline [12-141 and single crystal (111) [15] electrodes in chloride-containing electrolytes show, in the potential range mentioned above, the appearance of a small, reversible peak before the massive formation of AgCl, involving a charge smaller than a monolayer of AgCl. This peak has been attributed [13] to the formation of a submonolayer of adsorbed AgCl. It has also been found that the charge and the peak potential depend strongly on the pretreatment of the electrode. Hubbard and co-workers [15] have shown by LEED and Auger spectroscopies that on silver (111) this peak corresponds to a transition from a diffuse (1 X 1) to an ordered Ag (111) structure, (6 X fi)R30”. Valette and Parsons [lo], from the charge dependence of the amount of specifically adsorbed chloride on (110) single silver crystals, have proposed a structure of c(5 X 2) for the adsorbed chloride at the potential of the narrow peak in the C vs. E curve. In this paper we will show that the appearance of this peak is connected with profound changes of the capacitative response of evaporated thin silver film electrodes.