Oxygen electroreduction reaction complexities

Ab initio modeling of charge transfer process in the oxygen electroreduction reaction (OER) has achieved some notable stepwise progresses in complexity and in proximity to realistic systems. Initial models only involved a few Pt and reactant atoms. Later, a catalyst slab replaced the Pt cluster. The... 

Nowadays, it has been demonstrated that the reaction is indeed structure sensitive with a multielectron transfer process that involves several steps and the possible existence of several adsorption intermediates [93-96]. The main advantage that we have with the new procedures with respect to cleanliness is that we have well-ordered surfaces to study a complex mechanism such as the oxygen electroreduction reaction [96-99]. In aqueous solutions, the four-electron oxygen reduction appears to occur by two overall pathways a direct four-electron reduction and a peroxide pathway. The latter pathway involves hydrogen peroxide as an intermediate and can undergo either further reduction or decomposition in acid solutions to yield water as the final product. This type of generic model of a reaction has been extensively studied since the early 1960s by different authors [100-108]. 

The electrochemical intercalation of Li was studied for carbon electrodes modified by the 2Co-Ni complex, which showed the best effect in the reaction of oxygen electroreduction. Galvanostatic charge-discharge technique (PC governed automatic bench) in 2016 coin type cells was used for this purpose. 

The change in transition states with electrode potential is observed, for instance, in the complex 4-electron reaction of oxygen electroreduction on several electrode materials, the mechanism of which may also change with pH. At low negative overpotentials, the rds is reaction (124) with reaction (123) in pre-equilibrium. 

Cobalt catalyst precursors are cobalt(III) or cobalt(II) salts ligated to nitrogen and eventually oxygen-containing polydentate molecules like B12, salen, C2(DO)(DOH)p . The III/II electroreduction occurs at around OV vs SCE. Further reduction at ca. — 1 V vs SCE corresponds to the formation of cobalt(I) complexes which are the reactive species involved in the reactions mentioned below. 

The electroreduction of oxygen by N4-macrocylic complexes reaction is very sensitive to the nature of the metal center in the complex. Eor Ee and Mn phfhalocyanines, at low overpotentials a four-electron reduction is observed with rupture of the 0-0 bond [14, 81-83], without the formaticai of peroxide. In contrast Co, Ni, and Cu phthalocyanines promote the reduction of O2 only via two electrons to give peroxide... 

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