Structure and composition of the Ag (111) surface as a function of electrode potential in aqueous halide solutions

Abstract

Studies by means of Auger spectroscopy, LEED and voltammetry are reported of the surface layers which were formed when a well-defined Ag (111) surface was immersed into aqueous halide solutions (KF, KCl, KBr or KI) at controlled pH and electrode potential. Electrode potentials spanning the range from water reduction to silver oxidation were studied at pH 4 and 10. Surface composition (F, Cl, Br or I, O, K and Ag) was monitored as a function of electrode potential by means of Auger spectroscopy following immersion. Strong adsorption of Cl, Br and I but not F occurred throughout most of the potential range, including simple immersion at open-circuit. Strength of adsorption of Cl and Br diminished significantly at extremely negative potentials near the solvent-reduction limit at pH 10; however, iodide was adsorbed strongly at all potentials studied. Reductive desorption of Cl and Br from Ag (111) involved transfer of one electron per halogen atom in a very broad voltammetric peak spanning much of the accessible potential range, Cl and Br formed Ag (111) ( ▪)R30° structures, while iodide yielded some of the same complex structures as reported for Ag deposition at iodine-pretreated Pt (111). That is, the silver surface is reconstructed in I − solutions.