Studies are reported in which surface layers formed by immersion of well-defined Pt(lll) and Pt(100) electrode surfaces into aqueous Na2S solutions were characterized with regard to structure, composition, and reactivity by means of low-energy electron diffraction (LEED), Auger electron spectroscopy, electron energy-loss spectroscopy (EELS), linear scan voltammetry, and coulometry. Voltammetry reveals that only oxidative desorption of S occurs on the Pt surfaces; no S reductive desorption is observed over the useful potential range. Combined surface analysis data (Auger), vibrational spectra (EELS), and structural data (LEED) permit identification of adsorbed layer composition and structure on the Pt(lll) and Pt(100) surfaces as a function of potential. At potentials between -0.6 and 0.0 V (vs Ag/AgCl), LEED reveals that stable ordered adsorbed sulfur layers are formed on both surfaces: Pt(lll)(✓3X✓3)R30o-S and Pt-(100)(✓2X✓v2)R45°-S. The best clarity of the LEED patterns is found at pH 9. Potentials more positive than 0.0 V give rise to increasingly diffuse intensity related to oxidative desorption of S. Voltammograms for oxidative desorption of S from both surfaces are markedly different, indicating different mechanisms of S oxidation at the two surfaces: at pH 9, four voltammetric peaks are present for S at the Pt(111) surface, compared with only one peak for the Pt(100) surface. Coulometric data reveal that approximately six electrons are transferred in oxidation of adsorbed S at both surfaces at pH less than 10. Voltammetric behavior of the sulfur layer is sharply dependent upon pH.
All Science Journal Classification (ASJC) codes
- Materials Science(all)
- Condensed Matter Physics
- Surfaces and Interfaces