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Degree

Doctor of Philosophy, Case Western Reserve University, Chemistry, 1992.

Abstract

The objective of this thesis research is to understand the role of adsorbed species in various electrocatalytic processes using electrochemical techniques and in situ Fourier transform infrared reflection absorption spectroscopy (FTIRRAS). The work focuses on three types of electrode processes, all of which involve adsorbed species as reactants, intermediates or products, or function even as catalysts. They are (1) CO₂ electroreduction to CO on Pt, (2) O₂ reduction catalyzed by adsorbed transition metal tetra-sulfonated phthalocyanines (MeTsPc, Me = Co and Fe) and (3) the reduction of self-assembled layers of N-ethyl-N′-octadecyl-4,4′-bipyridinium (EOB) on metal surfaces. The electroreduction of CO₂ was studied on both polycrystalline and single crystalline platinum electrodes in acid solutions using electrochemical and FTIRRAS techniques. The catalytic activity of Pt and the product distribution were found to be dependent on the surface plane. Various effects on the CO₂ reduction reaction were examined including the variation of pH and electrode rotation rate, deuteration of the acid solution and the presence of impurities. Mechanistic pathways and reaction kinetics are discussed. The determination of the diffus ion coefficient of CO₂ in acid solutions using the FTIRRAS technique was demonstrated. FeTsPc was investigated on silver surfaces in an N₂-saturated 0.1 M HClO₄ solution using FTIRRAS. The orientation of FeTsPc on the electrode surface was discussed as a function of potential and oxidation state. The catalytic activity and stability for O₂ reduction of CoTsPc adsorbed on ordinary pyrolytic graphite (OPG) electrodes in acid solutions were found to be greatly improved in the presence of a coating of poly(4-vinylpyridine) (PVP). This may be explained in terms of the interactions between the PVP and CoTsPc. The structure and orientation of self-assembled layers of EOB on metal electrode surfaces (Pt, Au and Ag) were monitored as a function of potential with in situ FTIRRAS in aqueous solutions. The results obtained indicate that upon reduction of the EOB either undergoes dimerization or otherwise interacts electronically with the electrode surface or other ions in the solution, giving rise to vibronically coupled allowed modes which are ordinarily IR forbidden. Effects of the anion of the supporting electrolyte on the electrochemical behavior of the EOB layer were examined.

Subject Headings

Chemistry, Physical

Keywords

adsorbed species electrocatalytic processes Electrochemical situ infrared spectroscopic studies

Advisor

Ernest B. Yeager

Pages

274p.

Document number: case1056050643
Permalink: http://rave.ohiolink.edu/etdc/view?acc_num=case1056050643

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