Comparison of the Behavior of Several Cobalt Porphyrins as Electrocatalysts for the Reduction of O₂ at Graphite Electrodes

Abstract

Four cobalt porphyrins were adsorbed on graphite electrodes and used to catalyze the electroreduction of O2. The two porphyrins without substituent groups in the meso positions of the porphyrin ring operated at the most positive potentials and catalyzed the reduction of O2 to both H2O2 and H2O, but the H2O did not result from significant reduction of H2O2. The porphyrins containing meso substituents catalyzed only the reduction of O2 to H2O2. The catalysts that accomplish the four-electron reduction of O2 are argued to consist of dimeric (or higher oligomeric) forms of the adsorbed porphyrins. The present results and those of two recent related studies 1,2 indicate that the presence of only hydrogen or small alkyl groups in the meso positions of porphyrin rings facilitates the spontaneous formation of van der Waals dimers with greater catalytic activity for the reduction of O2 by four electrons. Such cobalt porphyrins were also found to be unusually active catalysts for the electro-oxidation of H2O2.

Enhancement of oxygen reduction at Co-porphyrin catalyst by supporting onto hybrid multi-layered film of polypyrrole and polyoxometalate-modified gold nanoparticles

“…Moreover, the Dedicated to Professor Jose Zagal on occasion of his 65th birthday. cobalt porphine, protoporphyrin IX and 5,10,15,20-tetramethylporphyrin, were successfully employed to drive efficiently the reduction of oxygen [5,11]. Some reports postulated high catalytic activity of face-to-face porphyrins toward the oxygen reduction reaction to water [12].…”

Electrochemical evidence of catalysis of oxygen reduction at the polarized liquid–liquid interface by tetraphenylporphyrin monoacid and diacid

“…bimetallic, heme/Cu catalytic site in cytochrome c oxidase [1,2]. Their synthetic analogues have been used to activate molecular oxygen for the O 2 reduction to hydrogen peroxide (H 2 O 2 ) and/or to water in the solution [3], at the solid electrodes [4], or at the polarized liquid-liquid interfaces [5,6]. The activation process involves the binding of O 2 to the metal center, and the electron delocalization from the metal to O 2 , which can be viewed like a coordinated superoxide or peroxide anion, i.e., as a Brønsted base [1,2].…”

“…Evidence for catalysis comes from ion transfer voltammetry at the water|DCE interface using acidified Li 2 SO 4 and bis(triphenylphosphoranylidene)ammonium tetrakis(4-chloro-phenyl)borate (BTPPATPBCl) as the supporting electrolytes in water and DCE, respectively. Both water and DCE solutions were saturated with air and contained 0.25 mM O 2 [7] and 1.39 mM O 2 [8], respectively.…”

Molecular Materials and Devices: Developing New Functional Systems Based on the Coordination Chemistry Approach

“…124 Outstanding research in this area has been carried out by Anson and co-workers along the last twenty years. [125][126][127] Collman and co-workers [128][129][130][131] have shown that the simultaneous interaction of the O 2 molecule with two CoP centers is involved in the activation by a cofacial biscobaltporphyrin. However, more recently, they found out that the change of the electrode material from pyrolytic graphite to gold can switch the mechanism from tetraelec- 6,2003 tronic to bielectronic.…”