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Heterogeneous reaction mechanism, anodic

Application of equation (4) to the organic cocktail oxidation profiles, given in Fig. 6(a), yields straight line plots. Two of these kinetic plots for current densities of 0.14 and 0.40 A cm are presented in Fig. 8. The linear relationships obtained demonstrate that pseudo first-order kinetics are obeyed. This relationship directly supports the heterogeneous bimolecular reaction mechanism proposed for the electrochemical oxidation of organics in the electrochemical reactor. The slopes of the linear plots yield the pseudo first-order rate constants, which are summarized in Table 2 for each value of the current density (i.e. the anodic electrode potential) used. It can be seen from the table that, with increasing current... [Pg.6]

Corrosion processes occurring at a met-al/electrolyte solution interface are heterogeneous electrochemical reactions. When metal is in contact with an aqueous electrolyte solution, two (or more) electrode reactions may occur simultaneously, and this can be considered as a mixed electrode system. Anodic and cathodic areas are spatially separated in a corrosion cell, where the partial electrode reaction mechanism is usually not known in detail. [Pg.475]

The electrochemical redox reaction of a substrate resulting from the heterogeneous electron transfer from the electrode to this substrate (cathodic reduction) or the opposite (anodic oxidation) is said to be electrochemically reversible if it occurs at the Nernstian redox potential without surtension (overpotential). This is the case if the heterogeneous electron transfer is fast, i.e. there must not be a significant structural change in the substrate upon electron transfer. Any structural change slows down the electron transfer. When the rate of heterogeneous electron transfer is within the time scale of the electrochemical experiment, the electrochemical process is fast (reversible). In the opposite case, it appears to be slow (electrochemically irreversible). Structural transformations are accompanied by a slow electron transfer (slow E), except if this transformation occms after electron transfer (EC mechanism). [Pg.1445]

Reoxidation of the cosubstrate at an appropriate electrode surface will lead to the generation of a current that is proportional to the concentration of the substrate, hence the coenzyme can be used as a kind of mediator. The formal potential of the NADH/NAD couple is - 560 mV vs. SCE (KCl-saturated calomel electrode) at pH 7, but for the oxidation of reduced nicotinamide adenine dinucleotide (NADH) at unmodified platinum electrodes potentials >750 mV vs. SCE have to be applied [142] and on carbon electrodes potentials of 550-700 mV vs. SCE [143]. Under these conditions the oxidation proceeds via radical intermediates facilitating dimerization of the coenzyme and forming side-products. In the anodic oxidation of NADH the initial step is an irreversible heterogeneous electron transfer. The resulting cation radical NADH + looses a proton in a first-order reaction to form the neutral radical NAD, which may participate in a second electron transfer (ECE mechanism) or may react with NADH (disproportionation) to yield NAD [144]. The irreversibility of the first electron transfer seems to be the reason for the high overpotential required in comparison with the enzymatically determined oxidation potential. [Pg.44]

Besides electrokinetic transport, chemical reactions also occur at the electrode surfaces (i.e., water electrolysis reactions with production of at the anode and OH at the cathode). Common mass-transport mechanisms like diffusion or convection and physical and chemical interactions of the species with the medium also occur. In a low-permeable porous medium under an electrical field, the major transport mechanism through the soil matrix during treatment for nonionic chemical species consists mainly of electro-osmosis, electrophoresis, molecular diffusion, hydrodynamic dispersion (molecular diffusion and dispersion varying with the heterogeneity of soils and fluid velocity [8]), sorption/ desorption, and chemical or biochemical reactions. Since related experiments are conducted in a relatively short period of time, the chemical and biochemical reactions that occur in the soil water are neglected [9]. [Pg.739]

The redox reactions associated with corrosion are invariably linked with local changes in pH, with metal oxidation reactions leading to a decrease in pH (since metal ions in aqueous solution are Lewis acids and undergo hydrolysis) and cathodic reactions leading to an increase in pH (e.g ff, H2O, and/or O2 reduction reactions). Thus, for localized corrosion where anodic and cathodic reactions occur at different sites on a metal surface, measurement of the pH distribution across the surface provides useful details about corrosion mechanisms. Variations in local pH often correlate with the heterogeneous microstructure of a metal alloy surface, since such microstructure influences the location of local anodes and cathodes on the surface. [Pg.472]


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Anode reaction mechanism

Anode reactions

Anodic reactions

Heterogeneous reaction

Heterogeneous reactions mechanism

Reaction heterogeneous reactions

Reaction mechanisms heterogenous

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