TY - JOUR
T1 - Electrocatalysis of dioxygen reduction in aqueous acid and base by multimolecular layer films of electropolymerized cobalt tetra(o-aminophenyl)porphyrin
AU - Bettelheim, A.
AU - White, B. A.
AU - Murray, Royce W.
N1 - Funding Information:
This research was supported in part by a grant from the National Science Foundation.
PY - 1987/2/10
Y1 - 1987/2/10
N2 - 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.
AB - 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.
UR - http://www.scopus.com/inward/record.url?scp=0001369007&partnerID=8YFLogxK
U2 - 10.1016/0022-0728(87)80224-3
DO - 10.1016/0022-0728(87)80224-3
M3 - Article
AN - SCOPUS:0001369007
SN - 0022-0728
VL - 217
SP - 271
EP - 286
JO - Journal of Electroanalytical Chemistry
JF - Journal of Electroanalytical Chemistry
IS - 2
ER -