Accession Number : ADA309228

Title :   Electrochemistry of Sulfur Adlayers on the Low-Index Faces of Silver.

Descriptive Note : Rept. for Jun 95-Mar 96,

Corporate Author : UTAH UNIV SALT LAKE CITY DEPT OF CHEMISTRY

Personal Author(s) : Hatchett, David W. ; White, Henry S.

PDF Url : ADA309228

Report Date : MAY 1996

Pagination or Media Count : 21

Abstract : The formation and reactivity of sulfur adlayers on single-crystal Ag electrodes ((111), (110), and (100) orientations) in aqueous solutions (pH = 13) containing HS(-) is reported. Oxidative adsorption of HS(-) (Ag + HS(-) (right arrow) AgSH + e(-)) occurs on all three low-index surfaces at potentials ranging between -0.5 and -0.7V of the thermodynamic value for bulk Ag2S formation. Voltammetric and electrochemical quartz crystal measurements demonstrate that the resulting AgSH adlayer undergoes a second one-electron oxidation (AgSH + Ag + OH(-) (right arrow) Ag2S + H2O + e(-)) at the (111) and (110) surfaces prior to bulk Ag2S formation, yielding an underpotential deposited Ag2S adlayer (surface coverages (S/Ag): theta Ag(111) = 0.46 +/- 0.02 and theta Ag(110) = 0.54 +/- 0.03). In contrast, the AgSH adlayer on Ag(100) is chemically inert prior to bulk Ag2S formation. Structural models indicate that the formation of a nearly stoichiometric Ag2S adlayer (i.e., theta approx. 0.5) is feasible on the (111) and (110) surfaces without significant reconstruction of the outermost atomic layers of the substrate, but not on the (100) surface. The results suggest that the formation of a Ag2S monolayer is allowed only when the number density of S and Ag atoms at the interface is nearly coincident with the reaction stoichiometry.

Descriptors :   *ELECTROCHEMISTRY, *SUBSTRATES, *SULFUR, *SILVER, *STOICHIOMETRY, REPRINTS, DENSITY, MEASUREMENT, MODELS, SOLUTIONS(MIXTURES), INTERFACES, LAYERS, STRUCTURAL PROPERTIES, THERMODYNAMICS, WATER, ADSORPTION, REACTIVITIES, SINGLE CRYSTALS, CRYSTALS, ATOMS, SURFACES, QUARTZ, ELECTRODES, VOLTAMMETRY.

Subject Categories : Inorganic Chemistry
      Physical Chemistry
      Crystallography
      Electricity and Magnetism

Distribution Statement : APPROVED FOR PUBLIC RELEASE