Catalysis of the Electroreduction of Dioxygen by Monomeric and Dimeric Cobalt Porphyrins

Citation

Durand, Richard Raymond, Jr. (1984) Catalysis of the Electroreduction of Dioxygen by Monomeric and Dimeric Cobalt Porphyrins. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/h738-ft41. https://resolver.caltech.edu/CaltechTHESIS:10072016-152635305

Abstract

Mechanistic aspects of the catalytic electroreduction of dioxygen by monomeric and dimeric cobalt porphyrins were investigated. The catalysts were examined while either adsorbed to graphite electrodes or dissolved in concentrated acids.

Monomeric cobalt(II) porphyrins adsorbed to graphite electrodes were found to reduce dioxygen to hydrogen peroxide. Cyclic and rotating disk voltammetry were used to examine the kinetics and mechanism of the catalyzed reactions. These monomeric catalysts exhibited behavior atypical of simple redox catalysis.

The mechanisms by which the reduction of dioxygen at graphite electrodes is catalyzed by cofacial dicobalt and related porphyrins has been investigated. The products of the reductions, the electrode potential where the reduction proceeds and the mechanistic role of protons were among the topics examined. A comparison of the behavior of several new cofacial metalloporphyrins has led to a more detailed proposal for the mechanisms by which they operate.

Monomeric and dimeric cobalt porphyrins have been dissolved in trifluoromethanesulfonic acid (5.6 M) and concentrated phosphoric acid without demetalation. The electrocatalytic reduction of dioxygen by solutions of the catalysts was examined by rotating disk and ring-disk voltammetry. The dissolved metalloporphyrins provide improved stability to the catalysts.

The reaction of a cobalt(II) complex with superoxide was examined electrochemically in a non-aqueous electrolyte. The affinity of superoxide for cobalt(II) has been demonstrated by cyclic voltammetry. The results of this study were related to mechanisms of dioxygen reduction in aqueous media.

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