Enhancement of the Catalytic Activity of a Macrocyclic Cobalt(II) Complex for the Electroreduction of O2 by Adsorption on Graphite

• Published in: Inorganic chemistry Vol. 35; no. 25; pp. 7253 - 7259
• Main Authors: Bhugun, Iqbal, Anson, Fred C
• Format: Journal Article
• Language: English
• Published: American Chemical Society 04.12.1996
• ISSN: 0020-1669; 1520-510X
• DOI: 10.1021/ic9608399

In solution, the [(tim)Co]2+ complex (tim = 2,3,9,10-tetramethyl-1,4,8,11-tetraazacyclotetradeca-1,3,8,10-tetraene) reacts only slowly with O2, but upon adsorption on graphite electrodes, it becomes an active catalyst for the reduction of O2 to H2O2. The electroreduction of O2 proceeds in a single voltammetric step at close to the diffusion-controlled rate at a relatively positive potential (0.25 V vs SCE). The remarkable enhancement in catalytic activity is attributed to a higher affinity for O2 of the adsorbed complex as a result of its interactions with functional groups on the surface of roughened or oxidized graphite. A possible mechanism for the catalytic reduction of O2 is proposed. It differs from the one employed by the analogous [(hmc)Co]2+ complex (hmc = C-meso-5,7,7,12,14,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane) which operates at less positive potentials and exhibits two separated voltammetric steps in the reduction of O2, via [(hmc)CoOOH]2+, to H2O2.