Cobalt octaethyltetrapyrazinoporphyrazine: Spectroscopy, and electrocatalytic and kinetic study of dioxygen reduction at a glassy carbon electrode

Cobalt octaethyltetrapyrazinoporphyrazine was synthesized and characterized by electronic absorption and magnetic circular dichroism spectroscopy. These spectroscopies and molecular orbital calculations within the framework of the Pariser-Parr-Pople approximation revealed that the effective π-conjugation system of octaethyltetrapyrazinoporphyrazine is smaller than phthalocyanines. For the first time, the electrochemical behaviour of cobalt octaethyltetrapyrazinoporphyrazine irreversibly adsorbed onto a glassy carbon electrode as a surface modifier is reported. The cobalt derivative/glassy carbon electrode showed catalytic activity for oxygen reduction. Surprisingly, the peak potentials for oxygen reduction at this electrode coincide well with those where Co^II is reduced to Co^I over the whole pH range, indicating that the active species for dioxygen reduction is Co^I rather than the Co^II species. A possible mechanism for the electrocatalysis of oxygen is discussed.