The electroreduction of oxygen was examined in aqueous solution containing iron or cobalt 4,4′,4″,4‴-tetracarboxyphthalocyanine (FeTCPc or CoTCPc). In the presence of FeTCPc ([FeTCPc] > ca. 3 × 10-5 M), oxygen was reduced quantitatively to water via hydrogen peroxide (H2O2) and the reaction could be explained by an electrochemical (EC) catalytic regeneration mechanism. In the presence of CoTCPc ([CoTCPc] > ca. 3 × 10-5 M), oxygen was reduced quantitatively to H2O2 at a potential closely coincident with that for CoII- to CoITCPc reduction, and moreover the resultant H2O2 was partially reduced to water at the same and more negative potentials. Magnetic circular dichroism and electronic absorption spectra have suggested that FeTCPc and CoTCPc as the reaction intermediates are low-spin divalent and low-spin monovalent complexes, respectively. The results are stated in comparison with those so far reported for iron and cobalt porphyrins and phthalocyanines.
ASJC Scopus subject areas
- Physical and Theoretical Chemistry