Anodic electrochemical pathway

Anodic electrochemical pathway can be explained as follows (acidic electrolytes) ... 

A layer that forms on top of a metal upon contact with the solution can be of three different types. If it is dense and nonconducting, it can protect the metal from further corrosion, but the system cannot be used as a battery, since the metal is totally isolated from the solution. If it is electronically and ionically conducting, reduction of the solvent at the film-electrolyte interface and oxidation of the metal at the metal-film interface can proceed freely, leading to a fast rate of self discharge. It is only when the film is both an ionic conductor and an electronic insulator that the chemical pathway of spontaneous reduction of the solvent at the anode is jirevented, whereas the electrochemical pathway of oxidation of the metal at the anode and reduction of the solvent at the cathode can proceed at a sufficient rate to allow the... 

In Scheme 8, five possible electrochemical pathways for the formation of V-acyli-minium ions are represented. Pathway a (see Sec. VIII.A) describes the direct anodic oxidation of amides and carbamates to the intermediated V-acylium ions via removal of one electron from the nitrogen lone pair followed by deprotonation in a-position of the nitrogen atom and further one-electron oxidation. In pathway b (see Sec. VIII.C), a decarboxylative methoxylation of an V-acylated amino acid (Hofer-Moset reaction) leads to the same intermediate. The radical that is formed after anodic decarboxylation is immediately further oxidized to the cation due to the electron donation of the nitrogen. Pathway c (see Sec. VIII.B) describes the anodic oxidation of an V-acylated amino... 

The advantages of the electrochemical pathway are that contamination with byproducts resulting from chemical reduction agents are avoided and that the products are easily isolated from the precipitate. The electrochemical preparation also provides a size-selective particle formation. Reetz et al. have conducted several experiments using a commercially available Pd sheet as the sacrificial anode and the surfactant as the electrolyte and stabilizer. Analysis of the (C8Hi7)4N Br-stabilized Pd ° particles produced have indicated that the particle size depends on such... 

In principle, electrochemical oxidation of carbon in acid occurs by at least two anodic reaction pathways (Atanassova, 2007) ... 

Many anodic oxidations involve an ECE pathway. For example, the neurotransmitter epinephrine can be oxidized to its quinone, which proceeds via cyclization to leukoadrenochrome. The latter can rapidly undergo electron transfer to form adrenochrome (5). The electrochemical oxidation of aniline is another classical example of an ECE pathway (6). The cation radical thus formed rapidly undergoes a dimerization reaction to yield an easily oxidized p-aminodiphenylamine product. Another example (of industrial relevance) is the reductive coupling of activated olefins to yield a radical anion, which reacts with the parent olefin to give a reducible dimer (7). If the chemical step is very fast (in comparison to the electron-transfer process), the system will behave as an EE mechanism (of two successive charge-transfer steps). Table 2-1 summarizes common electrochemical mechanisms involving coupled chemical reactions. Powerful cyclic voltammetric computational simulators, exploring the behavior of virtually any user-specific mechanism, have... 

The electrochemistry of single-crystal and polycrystalline pyrite electrodes in acidic and alkaline aqueous solutions has been investigated extensively. Emphasis has been laid on the complex anodic oxidation process of pyrite and its products, which appears to proceed via an autocatalytic pathway [160]. A number of investigations and reviews have been published on this subject [161]. Electrochemical corrosion has been observed in the dark on single crystals and, more drastically, on polycrystalline pyrite [162]. Overall, the electrochemical path for the corrosion of n-EeS2 pyrite in water under illumination has been described as a 15 h" reaction ... 

The mechanism of anodic chlorine evolution has been studied by many scientists. In many respects this reaction is reminiscent of hydrogen evolution. The analogous pathways are possible. The most probable one is the second pathway, in which the adsorbed chlorine atoms produced are eliminated by electrochemical desorption, but sometimes the first pathway is also possible. As a rule the first step, which is discharge of the chloride ion, is the slow step. 

Wolter O, Willsau J, Heitbaum J. 1985. Reaction pathways of the anodic oxidation of formic acid on platinum evidenced by oxygen-18 labeling—A DEMS study. J Electrochem Soc 132 1635-1638. 

As mentioned above, the electrochemical oxidation of a diene yields 1,2- and 1,4-addition products when the reaction is carried out in the presence of a nucleophile such as methanol or acetic acid. When the oxidation is carried out in the absence of the nucleophile it usually yields a polymeric compound as the major product. The formation of a small amount of the Diels-Alder adduct is, however, observed when the reaction is carried out in CH2CI2 with graphite anode. One of the proposed reaction pathways is shown in equation 68, though it is not clear whether the cyclohexadienyl radical serves as a diene (as shown in equation 6) or a dienophile in the Diels-Alder reaction. 

The function of the electrolyte membrane is to facilitate transport of protons from anode to cathode and to serve as an effective barrier to reactant crossover. The electrodes host the electrochemical reactions within the catalyst layer and provide electronic conductivity, and pathways for reactant supply to the catalyst and removal of products from the catalyst [96], The GDL is a carbon paper of 0.2 0.5 mm thickness that provides rigidity and support to the membrane electrode assembly (MEA). It incorporates hydrophobic material that facilitates the product water drainage and prevents... 

The anode layer of polymer electrolyte membrane fuel cells typically includes a catalyst and a binder, often a dispersion of poly(tetraflu-oroethylene) or other hydrophobic polymers, and may also include a filler, e.g., acetylene black carbon. Anode layers may also contain a mixture of a catalyst, ionomer and binder. The presence of a ionomer in the catalyst layer effectively increases the electrochemically active surface area of the catalyst, which requires a ionically conductive pathway to the cathode catalyst to generate electric current (16). 

Figure 13 Reaction pathway for the electrochemical incineration of p-benzoqui-none at a Pt anode covered with a quaternary metal oxide film. (From Ref. 54.)...

When a net reaction proceeds in an electrochemical cell, oxidation occurs at one electrode (the anode) and reduction takes place at the other electrode (the cathode.) We can think of the cell as consisting of two half-cells joined together by an external circuit through which electrons flow and an internal pathway that allows ions to migrate between them so as to preserve electroneutrality. 

The constructive and desired pathway towards the product competes with the electrochemical incineration. At high current densities the mineralization dominates. Therefore, lower current densities will be beneficial for a synthetic and nondestructive transformation. The compartment of electrochemical transformation caused by hydroxyl or methoxyl radicals can be estimated in the range of a few micrometers close to the BDD anode. Mass transport has to be efficient since the migration of products out of the electrochemical scene into bulk is crucial for avoiding the overoxidation. Control of both competing and critical processes will either cause failure (mineralization) or provide the opportunity for selective electroorganic synthesis (Fig. 2). 

The dimer reduction product of wave I, in turn, exhibited a polarographic anodic wave with Ej/2 = —0.27 V in neutral aqueous medium. Anodic electrolysis at the crest of this wave led to regeneration of the parent pyrimidone-2 The pathway for electrochemical reduction of pyrimidone-2 is consequently as formulated in Scheme 2. 

In electrocatalysis, notable cases of formation of strongly bound species that are not, however, the kinetically involved intermediates in the main reaction pathway arise in the electrochemical oxidations of HCOOH, HCHO, and CH3OH at Pt anodes for those reagents, a self-poisoning intermediate, variably identified as chemisorbed CO, in bridged or linear double bonding to the electrode, or the species- C—OH, is involved (43) this species is not a principal kinetically involved intermediate in, for example, HCOOH oxidation, which proceeds at unpoisoned sites by the mechanism discussed in Section V,B,3. 

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