Accession Number : ADA294321

Title :   Electrochemistry of Sulfur Adlayers on Ag(111). Evidence for a Concentration- and Potential-Dependent Surface-Phase Transition.

Descriptive Note : Interim rept. Jun-Dec 94,

Corporate Author : UTAH UNIV SALT LAKE CITY DEPT OF CHEMISTRY

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

PDF Url : ADA294321

Report Date : 31 JAN 1995

Pagination or Media Count : 30

Abstract : The electrochemical deposition of sulfur adlayers on highly-oriented, thin-film Ag( 111) electrodes in aqueous solutions (pH = 13) containing-sodium sulfide, Na2S, is reported. Three voltammetric waves, corresponding to the stepwise formation of a sulfur adlayer, are observed at potentials negative of that necessary to induce bulk oxidation of Ag. The total charge obtained by voltammetric integration of the three voltammetric surface waves (206 + - 8 Micro C/sq cm) is equivalent to a sulfur adatom coverage of 1.14 x 10(exp -9) mol/sq cm, in agreement with expectations based on a complete Ag2S(sub ads) layer (Theta ^ 0.5). The dependencies of the voltammetric response on scan rate and Na2S concentration are used to support a multistep mechanism in which adsorption and oxidation of HS- yields a nearly complete layer of AgSH(sub ads), prior to a separate and kinetically slow surface- phase transition to an order Ag2Sads layer. The voltammetric wave corresponding to the transition of the AgSH(sub ads) layer to the ordered Ag2S(sub ads) layer is greatly diminished or absent in dilute Na2S solutions, suggesting that a critical sulfur surface concentration is required for the transition to occur. Sulfur desorption studies in solutions containing only supporting electrolyte (no sodium sulfide) also support the conclusion that the surface-phase transition is dependent on the surface concentration of adsorbed sulfur species, as well as the electrode potential. jg

Descriptors :   *SURFACE WAVES, *LAYERS, *PHASE TRANSFORMATIONS, *ELECTROCHEMISTRY, *SULFUR, *SILVER, SCANNING, SOLUTIONS(MIXTURES), WATER, ADSORPTION, THIN FILMS, RATES, SODIUM, DEPOSITION, OXIDATION, ELECTRODES, TRANSITIONS, SURFACE CHEMISTRY, ELECTROLYTES, VOLTAMMETRY, DESORPTION, CONCENTRATION(CHEMISTRY), SULFIDES, ADATOMS.

Subject Categories : Inorganic Chemistry
      Physical Chemistry
      Electricity and Magnetism
      Atomic and Molecular Physics and Spectroscopy

Distribution Statement : APPROVED FOR PUBLIC RELEASE