Oxygen electroreduction reaction hydrogen adsorption

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]. 

Platinum/ platinum family metals/ and silver are classified in the second group. The oxygen electroreduction on these metals occurs both directly to water and via intermediate formation of hydrogen peroxide. The hydrogen peroxide formed in the parallel reaction is decomposed by chemical or electrochemical mechanisms. The relation between the rates of these processes depends in a complicated way on the nature of the metal, the potential, the coverage of the electrode by the chemisorbed species, and their adsorption character. The polarization curves are characterized by a single wave with a limiting current close to the diffusion current for the four-electron process. 

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