CaltechTHESIS
  A Caltech Library Service

Electrocatalytic Reduction of Dioxygen at Chemically Modified Electrodes

Citation

Ni, Ching-Long (1987) Electrocatalytic Reduction of Dioxygen at Chemically Modified Electrodes. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/EPT0-NF02. https://resolver.caltech.edu/CaltechTHESIS:07102015-095638444

Abstract

The kinetics of the reduction of O2 by Ru(NH3)6+2 as catalyzed by cobalt(II) tetrakis(4-N-methylpyridyl)porphyrin are described both in homogeneous solution and when the reactants are confined to Nafion coatings on graphite electrodes. The catalytic mechanism is determined and the factors that can control the total reduction currents at Nafion-coated electrodes are specified. A kinetic zone diagram for analyzing the behavior of catalyst-mediator-substrate systems at polymer coated electrodes is presented and utilized in identifying the current-limiting processes. Good agreement is demonstrated between calculated and measured reduction currents at rotating disk electrodes. The experimental conditions that will yield the optimum performance of coated electrodes are discussed, and a relationship is derived for the optimal coating thickness.

The relation between the reduction potentials of adsorbed and unadsorbed cobalt(III) tetrakis(4-N-methylpyridyl)porphyrin and those where it catalyzes the electroreduction of dioxygen is described. There is an unusually large change in the formal potential of the Co(III) couple upon the adsorption of the porphyrin on the graphite electrode surface. The mechanism in which the (inevitably) adsorbed porphyrin catalyzes the reduction of O2 is in accord with a general mechanistic scheme proposed for most monomeric cobalt porphyrins.

Four new dimeric metalloporphyrins (prepared in the laboratory of Professor C. K. Chang) have the two porphyrin rings linked by an anthracene bridge attached to meso positions. The electrocatalytic behavior of the diporphyrins towards the reduction of O2 at graphite electrodes has been examined for the following combination of metal centers: Co-Cu, Co-Fe, Fe-Fe, Fe-H2. The Co-Cu diporphyrin catalyzes the reduction of O2 to H2O2 but no further. The other three catalysts all exhibit mixed reduction pathways leading to both H2O2 and H2O. However, the pathways that lead to H2O do not involve H2O2 as an intermediate. A possible mechanistic scheme is offered to account for the observed behavior.

Item Type:Thesis (Dissertation (Ph.D.))
Subject Keywords:Dioxygen Reduction
Degree Grantor:California Institute of Technology
Division:Chemistry and Chemical Engineering
Major Option:Chemistry
Thesis Availability:Public (worldwide access)
Research Advisor(s):
  • Anson, Fred C.
Thesis Committee:
  • Chan, Sunney I. (chair)
  • Schaefer, William P.
  • Grubbs, Robert H.
  • Anson, Fred C.
Defense Date:28 October 1986
Funders:
Funding AgencyGrant Number
CaltechUNSPECIFIED
Record Number:CaltechTHESIS:07102015-095638444
Persistent URL:https://resolver.caltech.edu/CaltechTHESIS:07102015-095638444
DOI:10.7907/EPT0-NF02
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:9057
Collection:CaltechTHESIS
Deposited By: Ben Perez
Deposited On:10 Jul 2015 17:40
Last Modified:18 Dec 2020 02:12

Thesis Files

[img]
Preview
PDF - Final Version
See Usage Policy.

25MB

Repository Staff Only: item control page