Multi-step electrode reactions oxidation

Finally, it should be stressed that organic electron transfers only rarely occur as isolated steps because of the high chemical reactivity of odd-electron species. Normally, they are part of multi-step mechanisms together with other types of elementary reaction, such as bond forming and breaking. In organic electrochemistry a useful shorthand nomenclature for electrode mechanisms denotes electrochemical (= electron transfer) steps by E and chemical ones by C, and it is appropriate to use the same notation for homogeneous electron-transfer mechanisms too. Thus, an example of a very common mechanism would be the ECEC sequence illustrated below by the Ce(IV) oxidation of an alkylaromatic compound (14-17) (Baciocchi et al., 1976,... 

Another mechanism for induced codeposition of Mo was suggested by Chassaing et al for electrodeposition of Mo-Ni alloys from citrate-ammonia electrolytes. Electrochemical impedance spectroscopy (EIS) measurements were carried out in order to better understand the different reactions occurring on the electrode surface during deposition. The proposed mechanism is based on a multi-step reduction of molybdate species. A M0O2 layer is formed via reduction of molybdate ion as in Eq. (42). Then, if free Ni is present in solution, this oxide can first combine at low polarization with Ni, following the reduction reaction ... 

In a staged multi-scale approach, the energetics and reaction rates obtained from these calculations can be used to develop coarse-grained models for simulating kinetics and thermodynamics of complex multi-step reactions on electrodes (for example see [25, 26, 27, 28, 29, 30]). Varying levels of complexity can be simulated on electrodes to introduce defects on electrode surfaces, composition of alloy electrodes, distribution of alloy electrode surfaces, particulate electrodes, etc. Monte Carlo methods can also be coupled with continuum transport/reaction models to correctly describe surfaces effects and provide accurate boundary conditions (for e.g. see Ref. [31]). In what follows, we briefly describe density functional theory calculations and kinetic Monte Carlo simulations to understand CO electro oxidation on Pt-based electrodes. 

Much of the effort on the electrooxidation of ethanol has been devoted mainly to identifying the adsorbed intermediates on the electrode and elucidating the reaction mechanism by means of various techniques, as differential electrochemical mass spectrometry, in situ Fourier transform infrared spectroscopy, and electrochemical thermal desorption mass spectroscopy. The established major products include CO2, acetaldehyde, and acetic acid, and it has been reported that methane and ethane have also been detected. Surface-adsorbed CO is still identified as the leading intermediate in ethanol electrooxidation, as it is in the methanol electrooxidation. Other surface intermediates include various Ci and C2 compounds such as ethoxy and acetyl [102]. There is general agreement that ethanol electrooxidation proceeds via a complex multi-step mechanism, which involves a number of adsorbed intermediates and also leads to different byproducts for incomplete ethanol oxidation, as shown in Figure 1.22. 

The hydrogen (H2)/oxygen (-02 ) anode/cathode combination is the most highly developed fuel cell. It continues to be an essential power source for manned space missions, which accounts for its advanced state of development. Beyond the practical problem of a gaseous fuel (H2), both electrode reactions require precious-metal catalysts (usually platinum supported on porous carbon electrodes). As indicated in earlier sections, electrochemistry is limited to pathways that involve one electron steps. Hence, the essential function of the electrocatalysts for H2 oxidation and -02- reduction is to provide such pathways for these multi-electron transformations. 

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