In this thesis, we focus on theoretical investigations on metal interfaces where many heterogeneous chemical reactions take place. Surface-enhanced Raman scattering (SERS) spectroscopy and the modern electrochemical methods are important in-situ techniques that have been widely employed for a variety of applications. Theoretical simulations have become an indispensable tool to infer the molecular details of interfacial structures that are not directly accessible from experimental measurements. In this context, we have proposed several new theoretical models for both SERS and interfacial electrochemistry, which allow us to provide molecular-level understanding of the interfacial structures under the realistic experimental conditions.   The first part of the thesis has addressed the basic theory of SERS that offers the vibrational structure of the interfacial molecules. It is well known that the huge enhancement of Raman intensity in this technique can be attributed to two independent factors, namely the physical and chemical enhancements. The former is resulted from the enhanced electromagnetic field induced by the plasmonic excitations, while the latter comes from the changing of interaction between the molecule and the surface. The interplay between these two enhancement factors, which has long been an issue of debate, is revealed in this thesis. They are coupled through molecular polarizability. A practical computational approach is proposed and used to demonstrate the importance of the coupling on different molecular systems. It is found that for certain systems the coupling factor can be as large as 106. This finding is of great importance towards a comprehensive understanding of the SERS mechanisms and a quantitative prediction of the enhancement factor.   The other part of the thesis is devoted to the theory of interfacial electrochemistry, in particular the effects of water solution. A novel protocol that combines classical molecular dynamics (MD) and the first principles density functional theory (DFT) calculations is proposed to address the statistical behavior of interfacial properties. Special attention has been paid to the work function of Pt(111) surface and CO adsorption energy on Pt(111) surface in aqueous solution. It has been found that in this case the work function of Pt surface illustrates a surprisingly broad distribution under the room temperature, sheds new light on the understanding of reaction activity of the surface. The proposed protocol is able to provide results in very good agreement with experiments and should be applied routinely in future studies. / <p>QC 20120515</p>

Thèse de doctorat : Sciences physiques : Faculté de sciences de Paris : 1863. / Titre provenant de l'écran-titre.

Thesis (Ph. D.)--University of Texas at Austin, 2000. / Vita. Includes bibliographical references (leaves 125-132). Available also in a digital version from Dissertation Abstracts.

Thesis (Ph. D.)--University of Texas at Austin, 2001. / Vita. Includes bibliographical references.

Thesis (Ph. D.)--University of Chicago, Dept. of Chemistry, August 2001. / Includes bibliographical references. Also available on the Internet.

Thesis (Ph. D.)--University of Hong Kong, 1988.

In this thesis the electrochemical reduction of nitrobenzene in a methanol / sulphuric acid electrolyte is studied. Major products are shown to be para-anisidine, ortho-anisidine, para-aminophenol and aniline. A simple reaction model is derived, based on the well accepted mechanism for nitrobenzene reduction. Kinetic constants are determined from experimental results using a laboratory scale glass cell. Predictions as to potential - current behaviour and product formation as a function of mass transport and current density are made. It is shown that the rate of mass transport and the current density are crucial parameters in determining the chemical yields of the products formed. High rates of mass transfer and low current densities favour para-anisidine formation, whilst aniline is preferred under poor mass transfer conditions and high current densities. Results from a bench scale parallel plate cell fit the model predictions for the conditions used. The use of packed and fluidised bed electrodes is also investigated for the production of para-anisidine. Using copper particles, serious dissolution is shown to occur which leads to an increased yield of aniline. The copper dissolution is shown to have an electro-catalytic effect for the reduction of nitrobenzene to aniline. Results using Monel as an electrode material showed an improvement over copper, but preferential dissolution of nickel occurred. On the basis of the work in this thesis, copper or Monel packed and fluidised bed electrodes are not suitable for the production of para-anisidine.

The flow, reactions and current in a porous rotating disk electrode (PRDE) is studied experimentally and theoretically. A PRDE is an electrochemically active porous disk mounted on a classic rotating disk electrode (RDE). For the oxidation of iodide, the measured current from a PRDE as a function of rotation rate shows much richer behavior than the flat RDE, including a sigmoidal dependence on the rotation rate that specifically depends on the geometry of the disk, its permeability, porosity and the fluid and reactant transport properties. It is found that when the complex behavior of the current is explained in terms of the ratio of the effective electrochemical reaction time to the residence time of the fluid in the porous disk all the data can be plotted onto a universal curve at high rotation rates. With this knowledge the PRDE is modeled analytically where the reactant transport is dominated by either advection or diffusion. When advection is dominant the current can be expressed in a simple algebraic form involving the dimensionless reaction time. The diffusion dominated regime is modeled utilizing a boundary layer theory. The current is found as a function of the rotation rate, reaction rate, permeability, diffusion coefficients, kinematic viscosity, and geometry of the disk. Combined with finite effects analysis, the two analytic models accurately describe the PRDE for the full range of its operation regardless of the geometry of the disk. Also, the dominant mass transfer mode transition point is identified. Additional experiments with ferrocenemethanol are carried out using PRDEs constructed by mounting various sized carbon fiber disks onto glassy carbon RDEs to complement previous experiments using iodide. The results validate the theories for the operation of the PRDE in the regimes of advection or diffusion dominated transport. A possible application of the PRDE system for measuring rock acidization and permeability is explored by developing analytic and numerical models for a nonconductive porous disk. This system exhibits regimes limited by different processes: diffusion, advection, and reaction. It is found that a one-dimensional analytic model incorporating the finite thickness of the porous disk and the surface reaction rate suffices to describe the system. / text

Advances in the application of bipolar electrodes (BPEs) for screening of electrocatalysts, localized activation of a single conductive electrode, the optical tracking of single particles interacting with an active electrode, and the introduction of microwires in paper-based analytical devices are described. In an original proof of concept study arrays of BPEs were used to determine the relative activity of model nanoparticle systems for the oxygen reduction reaction (ORR) by a simple optical readout: the electrodissolution of Ag microbands. The number of bands that dissolved during the screening procedure determined the relative activity of the materials. These screening results for model nanoparticle systems were related to traditional electrochemical experiments and showed a strong correlation. Building on that initial study, the BPE platform for screening ORR electrocatalyst candidates was improved so that more materials could be evaluated simultaneously by increasing the density of electrodes in the array, controlled compositional variations were prepared with the implementation of piezodispensing, and a different reporter, Cr, replaced Ag at the BPE anodes which reduced the risk of contamination and improved reliability of screening experiments. Further studies into the versatility of the screening platform have been carried out using non-noble metal systems for the hydrogen evolution reaction (HER), which has a long history of interest for electrochemists. A single conductive electrode material can be made to act as an array of electrodes by confining it at the intersection of two orthogonal microfluidic channels. By manipulating the direction and magnitude of the electric field in the device, faradaic reactions can be selectively localized on the BPE. An approach for optically tracking individual, insulating microparticles interacting with an active UME has been achieved. This approach brings new insight and understanding of single particle electrochemical studies. Finally, a method for incorporating microwires and mesh electrodes into paper-based electroanalytical devices is reported. This has many advantages over traditional screen-printed carbon electrodes that are traditionally used in paper-based devices. / text

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