Electrocatalysis of oxygen reduction. 5. Oxygen to hydrogen peroxide conversion by cobalt(II) tetrakis(N-methyl-4-pyridyl)porphyrin
Cobalt(III) tetrakis(N-methyl-4-pyridyl)porphyrin (abbreviated Co/sup III/TMPyP), although water soluble, adsorbs irreversibly on the surface of a highly polished glassy-carbon electrode. This porphyrin readily undergoes a one-electron reduction, either in solution or adsorbed, to produce the cobaltous form, which catalyzes the reduction of oxygen quantitatively to hydrogen peroxide. The pK/sub a1/ of Co/sup III/TMPyP is found to shift from a value of 6.0 for the solution to 2.0 for the adsorbed case. Thus, the electrode potential at which oxygen catalysis occurs is dependent on the pH and on the concentration ratio of the solution cobalt porphyrin to oxygen. However, at a pH of ca. 4 the redox potential of the solution CoTMPyP becomes more positive in value than that of the reversible O/sub 2//H/sub 2/O/sub 2/ potential so that the electrogenerated cobaltous porphyrin no longer catalyzes the reduction of oxygen. The potential of catalysis then shifts negatively to the adsorbed CoTMPyP, which, upon reduction, converts the O/sub 2/ to H/sub 2/O/sub 2/. The addition of thiocyanate ion to the solution can accelerate the rate of electron transfer from the electrode to the cobalt porphyrin. This addition, in low concentrations, can favorably affect the potential at which oxygen is catalytically reacted by decreasing the overpotential for the Co/sup III/TMPyP reduction. 53 references, 9 figures, 3 tables.
- Research Organization:
- Ohio State Univ., Columbus
- OSTI ID:
- 6035976
- Journal Information:
- Inorg. Chem.; (United States), Vol. 24:23
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
COBALT COMPLEXES
CATALYTIC EFFECTS
HYDROGEN PEROXIDE
CHEMICAL PREPARATION
OXYGEN
REDUCTION
PORPHYRINS
PYRIDINES
CATALYSIS
ELECTROCHEMISTRY
ELECTRODES
ELECTRON TRANSFER
EXPERIMENTAL DATA
PH VALUE
REDOX POTENTIAL
AZINES
CARBOXYLIC ACIDS
CHEMICAL REACTIONS
CHEMISTRY
COMPLEXES
DATA
ELEMENTS
HETEROCYCLIC ACIDS
HETEROCYCLIC COMPOUNDS
HYDROGEN COMPOUNDS
INFORMATION
NONMETALS
NUMERICAL DATA
ORGANIC ACIDS
ORGANIC COMPOUNDS
ORGANIC NITROGEN COMPOUNDS
OXYGEN COMPOUNDS
PEROXIDES
SYNTHESIS
TRANSITION ELEMENT COMPLEXES
400400* - Electrochemistry