Electrocatalysis of dioxygen reduction in aqueous acid and base by multimolecular layer films of electropolymerized cobalt tetra(o-aminophenyl)porphyrin

A. Bettelheim, B. A. White, Royce W. Murray

Research output: Contribution to journalArticlepeer-review

97 Scopus citations

Abstract

Films of cobalt(III) tetra(o-aminophenyl)porphyrin, poly-CoToAPP, electrooxidatively polymerized from acetonitriel solutions onto glassy carbon electrodes, exhibit two stable Co(III/II) cyclic voltammetric waves in 0.5 M H2SO4 and 1 M NaOH solutions. The more positive of the two waves predominates at low film coverages (a few monolayer equivalents); the more negative wave grows at high coverages (10-100 monolayers), especially in basic solutions. The two waves are ascribed to monomeric and to dimeric (or higher aggregate) poly-CoToAPP species, respectively, that are distributed unevenly within the film. Both waves exert pronounced catalysis of O2 reduction, but differently; rotated ring-disk voltammetry shows that H2O2 production at potentials of the first ("monomeric") wave is much greater than that at the second. Electrocatalytic O2 reduction in 1 M NaOH with low coverage films produces considerable H2O2, but high coverage films produce no detectable H2O2 and are stable for a minimum of 104 turnovers of the film sites. The "dimer" poly-CoToAPP in the outer part of high coverage films may serve an efficient dismutase-like action on H2O2 escaping from the principal O2 reduction pathway in the inner, "monomer" part of the film. The rate constant of the O2 reduction on low coverage films is ca. 1×105 M-1 s-1, in acid and in base. Results for acid solutions of Co(III)ToAPP(Cl) are also reported, for comparison to the polymer film results.

Original languageEnglish
Pages (from-to)271-286
Number of pages16
JournalJournal of Electroanalytical Chemistry
Volume217
Issue number2
DOIs
StatePublished - 10 Feb 1987
Externally publishedYes

ASJC Scopus subject areas

  • Analytical Chemistry
  • Chemical Engineering (all)
  • Electrochemistry

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