ELECTROCATALYTIC REDUCTION OF DIOXYGEN BY QUADRUPLY AZA BRIDGED CLOSELY INTERFACED COFACIAL BIS(5,10,15,20-TETRAPHENYLPORPHYRIN)S IN VARIOUS PH SOLUTIONS

The electrocatalytic reduction of dioxygen is investigated by cyclic v oltammetry and chronoamperometry at a glassy carbon electrode and a ca rbon microelectrode adsorbed with cobalt porphyrins in dioxygen-satura ted aqueous solutions of various pH. The reduction potential (E(p)) of dioxygen at chemically modified electrodes shows dependence on pH. El ectrochemical reduction of dioxygen at monomeric Co-1 or dimeric Co-2- 2 modified electrodes establishes a pathway of 2e(-) reduction to form hydrogen peroxide, but it carries out 4e(-) reduction of dioxygen to water at the electrode adsorbed with dimeric Co-2-3 or Co-2-4 in all p H solutions. The electrocatalytic pathway of dioxygen reduction by cof acial biscobalt porphyrins is independent of pH, but the E(p) of dioxy gen reduction is dependent on pH. The electrochemical reduction of dio xygen is irreversible and diffusion controlled. (C) 1996 Elsevier Scie nce Ltd. All rights reserved.