| Abstract
| - Cobalt porphyrins with arylsubstituents at the 5-, 10-, 15-, and 20-positions of the porphyrinring give poorly defined voltammetry when adsorbed on graphiteelectrodes where they catalyze the electroreduction of O2only to H2O2. By contrast, thecorresponding porphyrin with methyl instead of aryl substituents,CoTMP, exhibits clear voltammetry and catalyzes the electroreduction ofO2 to H2O at unusually positivepotentials.
- Unlike most simple, monomeric cobalt porphyrins, the cobalttetramethylporphyrin identified in the title catalyzesthe electroreduction of O2 to H2O instead ofH2O2. On graphite electrodes, coatings ofthe porphyrin preparedby irreversible adsorption from chloroform solutions catalyze theelectroreduction of O2 in aqueous HClO4atunusually positive potentials. Both the title porphyrin and thecorresponding unsubstituted cobalt porphine areargued to derive their activity as four-electron reduction catalystsfrom their propensity to form dimers (or higheraggregates) in solution and, presumptively, on the surface of graphiteelectrodes.
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