Electrocatalysis dioxygen

Anson FC, Ni CL, Saveant JM. 1985. Electrocatalysis at redox polymer electrodes with separation of the catalytic and charge propagation roles. Reduction of dioxygen to hydrogen peroxide as catalyzed by cobalt(II) tetrakis(4-A-methylpyridyl)porphyrin. J Am Chem Soc 107 3442. 

Buttry DA, Anson FC. 1984. New strategies for electrocatalysis at polymer-coated electrodes. Reduction of dioxygen by cobalt porphyrins immobilized in Nalion coatings on graphite electrodes. J Am Chem Soc 106 59. 

Electrocatalysis employing Co complexes as catalysts may have the complex in solution, adsorbed onto the electrode surface, or covalently bound to the electrode surface. This is exemplified with some selected examples. Cobalt(I) coordinatively unsaturated complexes of 2,2 -dipyridine promote the electrochemical oxidation of organic halides, the apparent rate constant showing a first order dependence on substrate concentration.1398,1399 Catalytic reduction of dioxygen has been observed on a glassy carbon electrode to which a cobalt(III) macrocycle tetraamine complex has been adsorbed.1400,1401... 

Electrocatalytic Reduction of Dioxygen and Hydrogen Peroxide These two processes must be emphasized because reduction of dioxygen, and eventually hydrogen peroxide, features the usually claimed pathway for reoxidation of reduced POMs after the participation of the latter in oxidation processes. As a consequence, electrocatalysis of dioxygen and hydrogen peroxide reduction is a valuable catalytic test with most new POMs [154, 156,161]. 

The molecule is very stable and can be sublimed [i]. Numerous metal phthalocyanines can reversibly bind molecules like, e.g., dioxygen at the metal ion. This can result in activation of internal bonds and subsequent facilitation of chemical reaction, in this case of dioxygen -> electroreduction. Thus these molecules have attracted attention as catalysts for various reactions, in particular dioxygen reduction in, e.g., fuel cells [ii], in general -> electrocatalysis [iii] and in -> sensors [iv]. Their strong coloration, which can be modified electrochemically by reduction/oxidation, suggests use in -> electrochromic devices [v]. 

The first accounts that seemed to give direct enzyme electrochemistry were the reports concerning a soluble blue Cu oxidase, laccase, which catalyzed the rapid four-electron reduction of dioxygen to water. An efficient electrocatalysis of O2 reduction by adsorbed fungal laccase on pyrolytic graphite, glassy carbon, and C02-treated carbon black electrodes was first described by Tarasevich and co-workers (48). Several control experiments were carried out to verify direct electron transfer from the electrode to the Cu sites of the enzyme. 

This chapter provides a critical review of transition metal macrocycles, both in intact and thermally activated forms, as electrocatalysts for dioxygen reduction in aqueous electrolytes. Fundamental aspects of electrocatalysis, oxygen reduction and transition metal macrocycles will be highlighted in this brief introduction, which should serve as background material for the subsequent more specialized sections. 

The macrocycles Co (111) (cyclam) and Fe( 111)TM PyP display high activity for dioxygen reduction and negligible affinity for carbonaceous surfaces providing close to ideal conditions to warrant analyses of electrochemical data within the strict homogeneous electrocatalysis framework. Their most salient features are summarized in the two sub-sections to follow. 

RRDE is significantly simpler than with conventional cyclic voltammetry data in quiescent solutions [88, 89]. As such, these forced convection systems have been widely used in the study of electrocatalysis in general. Of special interest are situations where the rate determining step is chemical (a) or electrochemical (B) (Scheme 3.7) [60], In particular, for an RDE at steady state, the rate at which the reactant is depleted at the interface must be equal to the rate at which it is replenished from the solution via convective mass transport. For a reaction first order in dioxygen this relationship reads ... 

Matsufuji, A., S. Nakazawa, and K. Yamamoto (2001). Electrocatalysis of the reduction of dioxygen by 7t-conjugated polymer complexes with dinuclear cobalt porphyrin. J. Inorg. Organomet. Polym. 11, 47-61. 

Gouerec, P, A. Biloul, O. Contamin, G. Scarbeck, M. Savy, J. M. Barbe, and R. Guilard (1995). Dioxygen reduction electrocatalysis in acid media Effect of peripheral ligand substitution on cobalt tetraphenylporphyrin, J. Electroanal. Chem. 398, 67-75. 

Bettelheim, A., B.A. White, and R.W. Murray (1987). Electrocatalysis of dioxygen reduction in aqueous acid and base by multimolecular layer films of electropolymerized cobalt tetra(ortho-aminophenyl)porphyrin. J. Electroanal. Chenu 217, 271-286. 

Bedioui, R, S. Guterriez Granados, C. Bied Charreton, and J. Devynck (1991). Biomimetic oxidation of hydrocarbons by dioxygen—electrocatalysis using polypyrrole-manganese porphyrin film modified electrodes. New J. Chem. 15, 939-941. 

Appleby AJ. Electrocatalysis of aqueous dioxygen reduction. J Electroanal Chem 1993 357 117-79. 

Yeager E. Dioxygen electrocatalysis mechanism in relation to catalyst structure. J Mol Catal 1986 38 5-25. 

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