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 Title: Adsorption of Anions on Platinum and Rhodium Single-Crystal Electrodes: Ultrahigh Vacuum Approach Author(s): Rhee, Choong Kyun Doctoral Committee Chair(s): Wieckowski, Andrzej Department / Program: Chemistry Discipline: Chemistry Degree Granting Institution: University of Illinois at Urbana-Champaign Degree: Ph.D. Genre: Dissertation Subject(s): Chemistry, Physical Abstract: This thesis presents results of ex situ ultrahigh vacuum (UHV) studies of adsorption of reversibly adsorbing anions and anion-like urea molecule on platinum and rhodium single crystal electrodes. It reports on the composition and structure of bisulfate and urea on Pt(111) and Pt(100) surfaces and on the reactivity of perchlorate on Rh(100), Rh(111) and Rh(poly) electrodes. The composition and structure of chloride adsorbed after perchlorate decomposition on rhodium is also determined.Specifically, adsorption of bisulfate on platinum single crystal electrodes has been confirmed by using Auger electron spectroscopy (AES). It is shown that the coverage is compatible with that obtained by in situ radiochemical measurements. Bisulfate adsorbed on the Pt(111) electrode creates $(\surd3$ x $\surd3)$ adlattice with a maximum coverage of 0.33. Such a structure has been observed in a broad range of solution concentrations. To the contrary, bisulfate adsorbed on Pt(100) does not contribute to ordered adlattice formation.The anion-like behavior of urea on Pt(100) and Pt(111) has been verified using voltammetry. Upon adsorption on Pt(100), urea undergoes one electron charge transfer and forms c(2 x 4) ordered structure with a 0.25 coverage. However, urea adsorbs on Pt(111) randomly and without a measurable charge transfer.Evidence for perchlorate reduction to chloride on Rh(100), Rh(111) and Rh(poly) has been found by using voltammetry and the UHV methodology. The reaction rate decreases in the order of Rh(100) $>$ Rh(poly) $>$ Rh(111) under transient condition, and in the order of Rh(100) $\approx$ Rh(poly) $>$ Rh(111) under steady-state conditions.Based upon the above observations, I conclude that the weak interactions of anionic species are strongly dependent on the nature of the electrode material (electronic factor) and on the electrode surface geometry (structural factor). Also, my work illustrates a successful application of UHV techniques for the molecular-level investigations of reversible adsorption. Issue Date: 1992 Type: Text Description: 152 p.Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 1992. URI: http://hdl.handle.net/2142/72273 Other Identifier(s): (UMI)AAI9305666 Date Available in IDEALS: 2014-12-17 Date Deposited: 1992
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