Electroreductive reaction

Nickel-bpy and nickel-pyridine catalytic systems have been applied to numerous electroreductive reactions,202 such as synthesis of ketones by heterocoupling of acyl and benzyl halides,210,213 addition of aryl bromides to activated alkenes,212,214 synthesis of conjugated dienes, unsaturated esters, ketones, and nitriles by homo- and cross-coupling involving alkenyl halides,215 reductive polymerization of aromatic and heteroaromatic dibromides,216-221 or cleavage of the C-0 bond in allyl ethers.222... 

As discussed earlier, it is generally observed that reductant oxidation occurs under kinetic control at least over the potential range of interest to electroless deposition. This indicates that the kinetics, or more specifically, the equivalent partial current densities for this reaction, should be the same for any catalytically active feature. On the other hand, it is well established that the O2 electroreduction reaction may proceed under conditions of diffusion control at a few hundred millivolts potential cathodic of the EIX value for this reaction even for relatively smooth electrocatalysts. This is particularly true for the classic Pd initiation catalyst used for electroless deposition, and is probably also likely for freshly-electrolessly-deposited catalysts such as Ni-P, Co-P and Cu. Thus, when O2 reduction becomes diffusion controlled at a large feature, i.e., one whose dimensions exceed the O2 diffusion layer thickness, the transport of O2 occurs under planar diffusion conditions (except for feature edges). 

Oxygen Electroreduction Reaction with an Emphasis on Charge Transfer at Metal/Water Interface... 

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... 

The effect of the parameter to (given by Eq. (7.83)) on the SWV curves is shown in Fig. 7.43 for a spherical electrode of 50-pm radius. Large to-values relate to the situation where the complexes of the reactant species A are more stable than those of species B, whereas the opposite situation is found for small to-values. As can be observed, the only influence of this parameter is the shift of the curves toward more negative potentials when to increases on account of the hindering of the electroreduction reaction caused by the stabilization of the oxidized species with respect to the reduced ones. The peak potential in SWV coincides with the half-wave potential such that... 

Berl reaction - electroreduction reaction of dioxygen (O2) resulting in the formation of hydrogen peroxide (H2O2) (in acidic solution) or hydrogen peroxide anions (HO2) (in alkaline solutions). 

With the aim of using them in an H2/O2 PEMFC, Lai et al. prepared composite films of Nafion- and PAni-containing Pt particles as electrocatalysts for the oxygen electroreduction reaction [19]. Films cast from a solution of PAni and Nafion containing chemically reduced Pt displayed good electrocatalytic activity compared to films without PAni. 

For very active catalysts such as platinum supported on carbon, the direct four-electron and the peroxide-producing reaction occur in parallel, the first on the catalyst, and the latter on carbon surface domains. Accordingly, it is possible to diminish the peroxide activity to the equilibrium value of reaction (19.29). In this case, the electrode potential would approach the equilibrium value for the overall four-electron electroreduction reaction (19.24). 

The stationary cathodic current-potential polarization curve of the OERR on pyrolytic graphite exhibits the Tafel slope —0.120 V per decade at 25°C, and the stoichiometric number is 2 for the O2 to OH2 electroreduction reaction. For glassy carbon, the Tafel slope is —0.060 V per decade , and the corresponding stoichiometric number is 1, as expected for reaction (19.26) [28]. The OERR is first order in O2 and zero order in OH for both carbons. 

FIGURE 1.10 Current intensity versus electrode potential voltammetric profile for platinum single crystals, Pt(100) (cooled in air) with blue lines, Pt(110) with black lines and Pt(lll) in red lines, in 0.5 M sulfuric acid solution run at 0.05 V s 1 at room temperature. A difference with respect to the early single crystal preparation method by Will [18] is that the ones reported here are those obtained by Clavilier early in 1980. After 50 years of the first paper by Will on the use of single crystals for the oxygen electroreduction reaction and his finding of the given preferred activities on (111) and (100) planes, the industry still uses polycrystalline surfaces. 

Effect of Crystallographic Orientation in the Oxygen Electroreduction Reaction.64... 

The electrocatalysis of the oxygen electroreduction reaction has been studied since the early days of electrochemistry and surface science, and since the importance of corrosion technology and fuel cells was realized. In the early 1960s, it was proved that the reaction was not structure sensitive [92] however, the problem of the preparation of clean and atomic ordered single crystal surfaces still remained. 

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]. 

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