Coadsorption of anions and ultra-thin metal films on single crystal electrodes
Sung, Yung-Eun
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Permalink
https://hdl.handle.net/2142/22528
Description
Title
Coadsorption of anions and ultra-thin metal films on single crystal electrodes
Author(s)
Sung, Yung-Eun
Issue Date
1996
Doctoral Committee Chair(s)
Wieckowski, Andrzej
Department of Study
Chemistry
Discipline
Chemistry
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Chemistry, Analytical
Chemistry, Physical
Language
eng
Abstract
This thesis describes results of a combined ultra-high vacuum (UHV)-electrochemistry instrument for structual and compositional surface analysis of anions and ultra-thin metallic films of copper and silver deposited on single crystal electrodes. The anion and metal coverages from the Auger electron spectroscopy (AES) measurements were compared with results obtained by in situ radiochemical and electrochemical data. Using Low Energy Electron Diffraction (LEED), the structures of anions/underpotential deposition (UPD) admetals were characterized in different electrodes and electrolytes. For the first time, it was shown that core-level electron energy loss spectra (CEELS) from adsorbed atomic and ionic adsorbates were electrode potential dependent.
Adsorption of (bi)sulfate anions on Au(111), Rh(111), and Pt(111) electrodes in sulfuric acid media was studied. Since the AES ratio of oxygen-to-sulfur in the sulfate adlattice was 4, and the S(LMM) AES transitions and S(L$\sb {2,3}$) CEELS spectra showed a characteristic S$\sp{6{+}}$ surface valency. Emersion of the electrode from clean H$\sb2$S0$\sb4$ solution to UHV produced a stable Me(111)($\surd3\times\surd$3)R30$\sp\circ$ (bi)sulfate surface structure with 0.33 ML coverage for Pt and Rh and 0.20 ML for the Au. The electron density on the adlattice sulfur was higher than that in the salt, evidently due to backdonation of electrons from the substrate to the adsorbate.
Cu UPD on single-crystal Au(111), Pt(111), and Rh(111) electrodes in sulfate-containing electrolytes was studied. A mixed ($\surd$3 x $\surd$3) phase consisting of 2/3 ML Cu and 1/3 ML sulfate was found at intermediate electrode potentials, delimited by phase transitions at both higher and lower potentials at Au and Pt electrodes. On Rh(111) however, the ($\surd$3 x $\surd$3)R30$\sp\circ$ specific to copper coverage and sulfate coadsorption, was not found. This observation, together with the shape of the Rh(111) cyclic voltammogram, different from Au(111) and Pt(111). In the study of interactions of sulfate anions with a Ag/Au(111) surface, silver formed two well-ordered structures, Au(111)p(3 x 3) and Au(111)p(5 x 5). As the potential was made more negative, a series of phase transformations occurred to the adlattice in a fluoric acid solution, from p(3 x 3) and p(5 x 5) to a compressed (5 x 5) and (6 x 6), and to (1 x 1).
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