Catalysis of dioxygen reduction at graphite electrodes by an adsorbed cobalt(ii) porphyrin

The electroreduction of dioxygen to hydrogen peroxide is catalyzed when the Co(II) porphyrin shown in Fig. 1 is adsorbed on the surface of graphite electrodes. The electroreduction of the adsorbed catalyst occurs at potentials well separated from those where the dioxygen is reduced showing that more than a simple redox catalysis is involved. The porphyrin also catalyzes the electro-oxidatoin of hydrogen peroxide. In 1 M NaOH catalyst-coated electrodes yield reversible, almost nernstian responses to the $\text{O}{}_2\text{O}{}_2\text{H}{}^{\mathrm{?}}$ couple. Cyclic and rotating disk voltammetry were used to examine the kinetics of the catalyzed reactions and mechanistic schemes are proposed to account for the observed kinetics.