Electrochemical series, development

Each metal or metal area will develop an electrode with a measurable electrical potential. This potential can be referenced to that of a standard hydrogen electrode, which by convention is set at zero. Thus, all metals have either a higher or lower potential compared to hydrogen, and a comparative list of metals can be produced indicating their relative nobility. This list is the galvanic or electrochemical series and measured as an electromotive force (EMF). 

The reducing powers of metals parallel their relative electrode potentials, i.e. potentials developed when the metal is in contact with a normal solution of its salts. The potential of hydrogen being equal to 0, the potentials or electrochemical series of some elements are as shown in Table 4. 

The potential difference developed between aluminium and stainless steel is about the same as that developed between aluminium and copper. The cathodic reaction is easier on copper oxide than that on the highly protective passive oxide of stainless steels. Then, it is not the difference of potential between anode and cathode which counts, but the facility and rate of every reaction. A bare metal is generally a much better cathode than one covered with an oxide. Aluminium is more active than zinc in the electrochemical series. Practically, zinc protects aluminium which becomes covered with an oxide film.20 All more noble metals accelerate corrosion similarly, except when a surface film (e.g., on lead) acts as a barrier to diffusion of oxygen or when the metal is a poor catalyst for reduction of oxygen. 

Chemical and Electrochemical Corrosion of Pile Materials Under Radiation, Since uranium is readily oxidized, it must be protected from the water by a sheath or coating. Also, for the external cooling, a lining tube must be placed in the graphite. With water as the coolant, these two (the sheath and tube) must be of the same material or of two materials close together in the electrochemical series to suppress electrochemical corrosion. Of the few suitable materials, which have low danger coefficients and are not attacked appreciably by hot water, etc., the most promising are, in order, beryllium and aluminimn. While the former is more desirable also for its hardness and resistance to wear, the limited supply of beryllium available plus the lack of commercial development make aluminium with its more extensive commercial production and development practically the only alternative, imtil such time as beryllium or beryllium-aluminimn alloys can compete or surpass aluminium or unless further corrosion tests prohibit the use of aluminium and force the development of Be or Be-Al. 

The first theory of electrolysis was developed by Grotthuss in 1805 and Davy in 1807 isolated alkali metals by electrolysis. Volta, thereafter developed the electrochemical series (he called them the contact series) and in 1811, Berzelius extended the electrochemical series to include non metals, and correctly established some of the scientific basis of inorganic chemistry. Volta not only produced the world s first battery and the electrochemical series, but he qualitatively differentiated between groups such as metals, carbon and some sulphides which conducted electricity without undergoing chemical change, this he called conductors of the first class and others such as salt solution which is decomposed by electric current, which he called conductors of the second class. Volta s electrochemical series, correctly identified the flow of current from the more electropositive to the less electropositive metal in his series, when connected with each other and a conductor of the second class . 

The aim of this overview is first to present the general principles of electrocatalysis by metal complexes, followed by a series of selected examples published over the last 20 years illustrating the major electrochemical reactions catalyzed by metal complexes and their potential applications in synthetic and biomimetic processes, and also in the development of sensory devices. The area of metal complex catalysts in electrochemical reactions was reviewed in 1990.1... 

Chemical and electrochemical reactions in condensed phases are generally quite complex processes only outer-sphere electron-transfer reactions are sufficiently simple that we have reached a fair understanding of them in terms of microscopic concepts. In this chapter we give a simple derivation of a semiclassical theory of outer-sphere electron-transfer reactions, which was first systematically developed by Marcus [1] and Hush [2] in a series of papers. A more advanced treatment will be presented in Chapter 19. 

Thus, electrochemical data involving both thermodynamic and kinetic parameters of hydrocarbons are available for only olefinic and aromatic jr-systems. The reduction of aromatics, in particular, had already attracted much interest in the late fifties and early sixties. The correlation between the reduction potentials and molecular-orbital (MO) energies of a series of aromatic hydrocarbons was one of the first successful applications of the Hiickel molecular orbital (HMO) theory, and allowed the development of a coherent picture of cathodic reduction [1], The early research on this subject has been reviewed several times [2-4],... 

Figure 10. Kleitz s reaction pathway model for solid-state gas-diffusion electrodes. Traditionally, losses in reversible work at an electrochemical interface can be described as a series of contiguous drops in electrical state along a current pathway, for example. A—E—B. However, if charge transfer at point E is limited by the availability of a neutral electroactive intermediate (in this case ad (b) sorbed oxygen at the interface), a thermodynamic (Nernstian) step in electrical state [d/j) develops, related to the displacement in concentration of that intermediate from equilibrium. In this way it is possible for irreversibilities along a current-independent pathway (in this case formation and transport of electroactive oxygen) to manifest themselves as electrical resistance. This type of chemical valve , as Kleitz calls it, may also involve a significant reservoir of intermediates that appears as a capacitance in transient measurements such as impedance. Portions of this image are adapted from ref 46. (Adapted with permission from ref 46. Copyright 1993 Rise National Laboratory, Denmark.)...

A series of nucleation and growth models was developed by, for example, Bewick et al. (11), Armstrong and Harrison (16), and Scharifker and Hills (17). Amblart et al. (18) have shown that nickel epitaxial growth starts with the formation of three-dimensional epitaxial crystallites. An electrochemical model for the process of electroless metal depositions (mixed-potential theory) was suggested by Paunovic (14) and Saito (14b). 

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