Integrating Experiment and Theory in Electrochemical Surface Science : Studies on the Molecular Adsorption on Noble-Metal Electrode Surfaces by Density Functional Theory, Electron Spectroscopy, and Electrochemistry /
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| Other Authors: | , |
| Format: | Thesis eBook |
| Language: | English |
| Published: |
[College Station, Texas] :
[Texas A & M University],
[2013]
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| Subjects: | |
| Online Access: | Link to OAK Trust copy |
| Abstract: | Computational techniques based on density functional theory (DFT) and experimental methods based on electrochemistry (EC), electrochemical scanning tunneling microscopy (EC-STM), and high-resolution electron energy loss spectroscopy (HREELS) were employed to study the adsorption of (i) sulfuric acid on Pd(111), (ii) benzene on Pd(111), (iii) hydroquinone/benzoquinone on Pd(111), (iv) hydroquinone sulfonate/benzoquinone sulfonate on Pd(111), (v) 2,3-dimethylhydroquinone/2,3-dimethylbenzoquinone on Pd(111) and polycrystalline Pd, (vi) hydrogen on 1-6 monolayers (ML) of Pd deposited on a Pt(111) substrate, and (vii) a thiolated iron hydrogenase model complex on polycrystalline Au. In situ EC-STM and DFT investigations of sulfuric acid on a Pd(111) surface indicated that two layers of water molecules and hydronium ions are assembled, non-co-planar with one another, between the rows of surface-coordinated sulfate anions; the layer that is slightly elevated is composed of hydronium counter cations. The STM images of benzene chemisorbed on a Pd(111) electrode surface were simulated and the results suggested that, when the potential of the Pd electrode is held at 0.3 V, benzene is chemisorbed on a 3-fold site; while at 0.55 V, the molecule is adsorbed on a position between a 3-fold and a 2-fold site. Computational and experimental results implied that at low concentrations, hydroquinone sulfonate undergoes oxidative chemisorption forming benzoquinone sulfonate (BQS) on the Pd(111) surface, BQS adopts a flat orientation in which the quinone ring is centered over a 2-fold site, and the C-H and C-S bonds are no longer co-planar with the quinone ring and are slightly tilted, directed away from the surface. At very dilute concentrations, when hydroquinone (H₂Q) undergoes oxidative chemisorption producing benzoquinone oriented flat, albeit with a slight tilt, on the Pd(111) surface, the flat-adsorbed quinone ring is centered on a bridge site where the C₂ axis is rotated 30⁰ from the [110] direction of the metal substrate, the p-oxygen atoms are located above two-fold sites, and the ring is slightly puckered with the C-H bonds tilted away from the surface at approximately 20⁰. When 2,3-dimethylH₂Q is chemisorbed on the Pd surface, at low concentrations, 2,3-dimethylH₂Q is oxidatively chemisorbed producing 2,3-dimethyl-1,4-benzoquinone oriented flat on the surface, the flat-adsorbed rings are centered above 2-fold sites wherein the C=O bonds are pointing 30⁰ from the [110] direction of the substrate, the para-oxygen atoms are located above bridge sites, the peripheral bonds are tilted away from the surface at ca. 20⁰, and at higher concentrations, oxidative chemisorption occurs through activation of the ring's C-H bonds yielding edge-oriented 2,3-dimethylH₂Q. Electrochemistry and DFT results also implied that at 1-2 ML of Pd on Pt(111), hydrogen is only adsorbed on a hollow site while at 3 ML of Pd or more, atomic hydrogen may be chemisorbed on the 3-fold site or absorbed in the octahedral hole underneath the hollow site. Using Au electrodes, an unbound iron hydrogenase analogue complex studied was found to slightly catalyze the H₂ evolution process. However, when the complex was immobilized unto the Au surface, the electrocatalytic activity was greatly improved. The electronic version of this dissertation is accessible from http://hdl.handle.net/1969.1/151363 |
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| Item Description: | "Major Subject: Chemistry." Includes vita. "Major Subject: Chemistry" |
| Physical Description: | 1 online resource. |
| Bibliography: | Includes bibliographical references. |