Adlayer structure and catalysis on single crystal electrodes

Si-Chung Chang, Purdue University

Abstract

I have utilized infrared reflection-absorption spectroscopy for in-situ molecular adsorbate characterization as well as mechanistic examination of electrocatalytic processes at monocrystalline metal-aqueous interfaces. The first part of the work is focused on the comparison with the behavior of metal surfaces in ultrahigh vacuum (uhv) systems and illustrated for the adsorption of carbon monoxide on low-index platinum and rhodium surfaces in aqueous media. The effects of altering the electrode potential on the C-O stretching frequencies and terminal/bridging binding-site geometries are rationalized in terms of chemical bonding models. Theoretical molecular orbital calculations on Rh (111) and Rh(100) in CO binding induced by both solvent and metal coadsorption are also examined. The central role of island formation during electrooxidation of CO adlayers on platinum and rhodium surfaces is implicated directly by the infrared data. The large effects of gold crystallographic orientation on the CO electrooxidation rates are discussed in terms of reactant adsorption and surface stereochemical factors. Second part of author's Ph.D. research is concerned of the catalytic electrooxidation of small organic molecules on both transition- and noble-metal surfaces. The electrochemical kinetics of formic acid, methanol, and ethanol in 0.1 M perchloric acid on Pt(111), Pt(100), Pt(110), and Rh(100) surfaces were examined by means of real-time infrared spectroscopic measurements. In some cases, the quantitative kinetics and mechanisms of competing electrochemical pathways for these electrooxidation processes can also be evaluated. The electrooxidation of polyfunctional alcohols have been examined on seven oriented gold electrodes, Au(111), (100), (110), (221), (533), (311), and (210), in aqueous 0.1 M acid. The major emphasis of such investigation is to understand the role of surface crystallographic orientation on the catalytic electrooxidation of these polyfunctional molecules. The results are compared with corresponding data for simple unifunctional reactants, especially for formic acid and carbon monoxide.

Degree

Ph.D.

Advisors

Weaver, Purdue University.

Subject Area

Analytical chemistry|Chemistry

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