Degree Type

Dissertation

Date of Award

1991

Degree Name

Doctor of Philosophy

Department

Chemistry

First Advisor

Dennis C. Johnson

Abstract

Voltammetry at rotated disk and rotated ring-disk electrodes was applied to the study of several aspects of anodic, oxygen-transfer reactions at noble electrodes. Anodic reactions which involve the transfer of oxygen from H[subscript]2O to the oxidation products generally exhibit a voltammetric response characterized by severe kinetic limitations. Mechanistic studies were performed at noble electrodes in order to contrive strategies for improving the kinetics of these reactions;Competitive adsorption studies were used to devise an adsorption hierarchy for Au rotated disk electrodes. It was concluded that adsorption was a prerequisite for oxidations involving the transfer of oxygen present on the electrode surface as adsorbed hydroxyl radicals;The electrogenerated chemiluminescence (ECL) of luminol was studied at Au, Pt, Pd, glassy carbon, PbO[subscript]2, and Bi-doped PbO[subscript]2 electrodes. The ECL intensity was determined to be inversely related to the electrochemical activity for the oxidation of luminol. It was concluded that the oxygen-transfer oxidation of luminol to 3-aminophthalate (n = 4 eq mol[superscript]-1) corresponded to the dark reaction, whereas the electron-transfer oxidation of luminol with n = 1 eq mol[superscript]-1 initiated the chemiluminescent reaction in solution. This mechanism is consistent with the inverse relationship observed between electrode activity and ECL intensity, and is in agreement with experimentally determined rate laws;It was demonstrated that many oxygen-transfer oxidations are catalyzed by adsorbed hydroxyl radicals present at noble metal electrodes during the oxidation of H[subscript]2O to O[subscript]2. For example, the overpotential for the oxygen-transfer oxidation of iodide to iodate was determined to be directly related to the overpotential for O[subscript]2 evolution at Au, Pt, Pd, Ir, and glassy carbon electrodes;Composite electrodes fabricated from mixtures of graphite, noble metals, and Kel-F were used to improve the current efficiency of oxygen-transfer oxidations which occurred during simultaneous anodic evolution of O[subscript]2. These electrodes functioned as microelectrode ensembles and, therefore, exhibited higher current densities than conventional electrodes. The current was independent of the rotation rate of the electrode at extremely low loadings of noble metal, indicating a regime where the sites behaved as isolated microelectrodes.

DOI

https://doi.org/10.31274/rtd-180813-11400

Publisher

Digital Repository @ Iowa State University, http://lib.dr.iastate.edu/

Copyright Owner

Joseph Edward Vitt

Language

en

Proquest ID

AAI9202404

File Format

application/pdf

File Size

187 pages

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