Electrochemical reactions classified

According to the literature [21], all reported electrochemical oscillations can be classified into four classes depending on the roles of the true electrode potential (or Helmholtz-layer potential, E). Electrochemical oscillations in which E plays no essential role and remains essentially constant are known as strictly potentiostatic (Class I) oscillations, which can be regarded as chemical oscillations containing electrochemical reactions. Electrochemical oscillations in which E is involved as an essential variable but not as the autocatalytic variable are known as S-NDR (Class II) oscillations, which arise from an S-shaped negative differential resistance (S-NDR) in the current density (/) versus E curve. Oscillations in which E is the autocatalytic variable are knovm as N-NDR (Class III) oscillations, which have an N-shaped NDR. Oscillations in which the N-NDR is obscured by a current increase from another process are knovm as hidden N-NDR (HN-NDR Class IV) oscillations. It is known that N-NDR oscillations are purely current oscillations, whereas HN-NDR oscillations occur in both current and potential. The HN-NDR oscillations can be further divided into three or four subcategories, depending on how the NDR is hidden. 

For catalysts, the roles of NPs can be classified by their end-use function. Electrochemical applications of catalytic NPs focus on two main functions enhancing an electrochemical reaction or assisting electron transfer at an electrode surface. Electrochemical reactions can occur at the NP core or the periphery, depending upon the design of the NP. However, electron transfer mechanisms can proceed through the core due to the conductivity of metallic NPs. 

In previous chapters, we dealt with various electrochemical processes in non-aque-ous solutions, by paying attention to solvent effects on them. Many electrochemical reactions that are not possible in aqueous solutions become possible by use of suitable non-aqueous or mixed solvents. However, in order for the solvents to display their advantages, they must be sufficiently pure. Impurities in the solvents often have a negative influence. Usually commercially available solvents are classified into several grades of purity. Some of the highest-grade solvents are pure enough for immediate use, but all others need purification before use. In this chapter, the effects of solvent impurities on electrochemical measurements are briefly reviewed in Section 10.1, popular methods used in solvent purification and tests of impurities are outlined in Sections 10.2 and 10.3, respectively, and, finally, practical purification procedures are described for 25 electrochemically important solvents in Section 10.4. 

In a restricted sense, corrosion is considered toconsistof the slow chemical and electrochemical reactions between melals and their environments. From a broader point of view corrosion is the slow destruction of any material by chemical agents and electrochemical reactions. This contrasts with erosion, which is the slow destruction of materials by mechanical agents. The character of the atmospheres to which materials arc exposed may he classified as rural, urban, industrial, urban-marine, industrial-marine, marine, tropical, and tropical-marine. In addition to these general kinds of environments, corrosion is of particular concern in the environments of chemical, petrochemical, and otherprocessing and manufacturing environments where extremely corrosive substances may be encountered. 

Electrochemical reactions can be classified by their reaction mechanisms. 

Organic electrochemical reactions are classified in the same way as other organic reactions [1,2]. The most important prototypes include additions (Scheme 6.1) [ 13,14], eliminations (Scheme 6.2) [15, 16], substitutions (Scheme 6.3) [17, 18], couplings and dimerisations (Scheme 6.4) [19-21], cleavages (Scheme 6.5) [22,23], and catalytic reactions (Scheme 6.6) [24,25]. Hundreds of other examples maybe found in the literature [1,2]. 

It is conventional to classify electrochemical reactions as outer-sphere and inner-sphere. The former involve the outer coordination sphere of a reacting ion. Thus, little if any change inside the ion solvate shell occurs they proceed without breaking-up intramolecular bonds. But in the latter, involving the inner coordination sphere, electron transfer is accompanied by breaking up or formation of such bonds. Often the inner-sphere reactions are complicated by adsorption of reactants and/or reaction products on the electrode surface. The electron transfer in the Fc(CN)62 /4 system is example of an outer-sphere reaction (with due reservation for some complications... 

Electrode processes are conveniently classified according to the nature of the final product1 and its formal mode of formation, since then the interplay between nucleophile(s) or electrophile(s), substrate, and loss or addition of electron(s) is best expressed. It is upon our ingenuity to choose the correct combination of electrolyte components that the practical success of an electrochemical reaction rests, and therefore the rather formalized classification system to be outlined and exemplified below is the logical point of departure into the maze of mechanistic intricacies of electrode processes. 

Thus, in general, a reduced and an oxidized product are obtained, in complete analogy with a classical electrochemical reaction. Except for a very few examples, almost all reactions photocatalyzed by semiconductors fall within this scheme and we have proposed to classify such reactions as semiconductor photocatalysis type A [45]. 

On the other hand, when one thinks in terms of electrochemical reductions or oxidations, special attention is devoted to the coreactant, that is, to the electrode that provides or accepts electrons. Thus, in order to discuss or compare electrochemical reactions with their organic analogs, it is of the utmost importance to use more precise terms than the so inaccurate reduction of oxidation notions. A similar problem has been addressed in the inorganic and organometallic fields. Indeed, it was early recognized that oxidation-reduction reactions at metal centers must be classified according to two types outer sphere or inner sphere reactions. A typical example of this dichotomy is given in Eqs. (14) and (15), which relate to chromium (II) oxidations by cobalt (III) complexes. 

Photoelectrochemical imaging systems may be roughly classified into two classes one is concerned with photoinduced electrochemical reaction systems using various electrode configurations and the other with light-induced heterogeneous reaction systems. The former may be... 

Generally, corrosion is classified in various ways. Basically, the corrosion phenomena involve electrochemical reactions as shown above. Water is always related to them. However, we can teU the difference when corrosion occurs in aqueous solutions and when it occurs in the atmosphere, even though the latter contains a... 

The general principles of electrochemistry are presented in reviews, books, and many ongoing series of reviews of "Advances in the Field". In regard to electroorganic chemistry, a useful introduction to the necessary concepts are the books by Fry nd a number of others. Scale-up for practical applications is addressed in a primer and further described in a more extensive volume on industrial electrochemistry. Electrochemical reactions in which a key process is the transfer of electrons at an electrode can be classified in three general types. 

As mentioned in early sections, redox flow batteries can be classified into different types based on electrochemical reactions occurring at the electrodes. Divided and undivided reactor configurations of redox flow batteries are shown in Figure 11. 

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