Electrocatalytic Reduction of Dioxygen to Water by Iridium Porphyrins Adsorbed on Edge Plane Graphite Electrodes

Abstract

A number of iridium porphyrins adsorbed on pyrolytic edge plane graphite electrodes have been examined for their electrocatalytic activity toward the four-electron reduction of dioxygen. Their behavior provides insight into the mechanisms by which the iridium porphyrins accomplish this electrocatalysis. Certain iridium porphyrins are found to reduce dioxygen to water via a four-electron pathway in a monometallic fashion. Axial ligation from the edge plane graphite electrode to the iridium metal center is believed to be essential for the catalytic reduction of dioxygen to occur. We propose the active species to be an Ir(II) center. The electrocatalytic behavior of all of the iridium porphyrins which have been examined can be explained by the transformation of these

Cobalt(IV) corroles as catalysts for the electroreduction of O2: Reactions of heterobimetallic dyads containing a face-to-face linked Fe(III) or Mn(III) porphyrin

“…This contrasts with monocobalt porphyrins which can act as four-electron reduction catalysts only through self-assembly on the electrode surface [16,[24][25][26][27][28]. Tetraruthenated cobalt meso-tetrakis(4-pyridyl)porphyrin complexes [15] as well as dimeric and monomeric iridium porphyrins have also been found to accomplish the heterogeneous reduction of O 2 to H 2 O [29].…”

Functional Analogs of Heme Protein Active Sites

“…Table 5 displays both thermodynamic and kinetic data for O 2 binding to the above-mentioned complexes and another atropisomer in which the acrylamide substituent has been rotated to the proximal face. 31 Before recounting our recent work, I need to outline the structure of CcO and the mechanism by which it is thought to operate. As shown in Figure 16, this phenomenon does not depend on the metal; it is also seen with structurally similar Co complexes.…”

The Rational Design of Time‐Dependent (“Mechanical”) Homogeneous Catalysts. A Literature Survey of Multicentered Homogeneous Catalysis

“…The use of other electrodes or incorporation within thin-layer porous polymers deposited on electrode surfaces leads to the exclusive production of H 2 O 2 [37]. As graphite is known to adsorb porphyrins strongly, electron transfer to the porphyrin is suggested to be faster using a graphite electrode than with other electrode materials [40]. If this hypothesis is correct, it supports the contention that the activated state of the key peroxide intermediate in 1 must be extremely short-lived-so short-lived that it can undergo O -O cleavage only when the complex is very rapidly supplied with an electron.…”