Electrode Catalysis of the Four-Electron Reduction of Oxygen to Water by Dicobalt Face-to-Face Porphyrins

Article abstract of DOI:10.1021/ja00539a009

A series of dimeric metalloporphyrin molecules has been synthesized in which the two porphyrin rings are constrained to lie parallel to one another by two amide bridges of varying length than link the rings together.These cofacial metalloporphyrins have been applied to the surface of graphite electrodes and tested for catalytic activity toward the electroreduction of dioxygen to water in aqueous acidic electrolytes.All molecules tested exhibited some catalytic activity, but hydrogen peroxide rather than water was the chief reduction product.However, the dicobalt cofacial porphyrin linked by four-atom bridges produced a catalyzed reduction almost exclusively to water and at exceptionally positive potentials.Rotating ring-disk voltammetric measurements were employed to diagnose the electrode reaction pathway and a possible mechanism for the observed catalysis is suggested.The results seem to demonstrate the participation of two metal centers in controlling the course of a multiple-electron process.