Electrochemistry of Sulfur Adlayers on Ag(111). Evidence for a Concentration- and Potential-Dependent Surface-Phase Transition.
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
Document Details
- Document Type
- Technical Report
- Publication Date
- Jan 31, 1995
- Accession Number
- ADA294321
Entities
People
- David W. Hatchett
- Henry S. White
- Xiaopong Gao
Organizations
- University of Utah