Electrochemistry, anodic oxidation

DespiC, A. Electrochemistry of Aluminum in Aqueous Solutions and Physics of Its Anodic Oxide 20... 

G. Foti, D. Gandini, and C. Comninellis, Anodic oxidation of organics on thermally prepared oxide electrodes, Current Topics in Electrochemistry 5, 71-91 (1997). 

It was also observed that, with the exception of polyacetylene, all important conducting polymers can be electrochemically produced by anodic oxidation moreover, in contrast to chemical methoconducting films are formed directly on the electrode. This stimulated research teams in the field of electrochemistry to study the electrosynthesis of these materials. Most recently, new fields of application, ranging from anti-corrosives through modified electrodes to microelectronic devices, have aroused electrochemists interest in this class of compounds... 

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 ... 

Compared with conjugated dienes, the electrochemistry of nonconjugated dienes is classified into two types, A and B11,12. In type A, the double bond of the diene behaves essentially the same as the double bond of a monoolefin in the anodic oxidation. A typical... 

The anodic oxidation of nitrogen compounds provides an excellent example of how the use of electrochemistry can alter the way in which we view the syntheses of complex organic molecules. Currently, there are two main thrusts to these efforts. First, the oxidation reactions allow for a reversal in the polarity of known functional groups, and therefore molecules with nucleophilic nitrogens can he converted into electrophiles. Second, the oxidation reactions allow for the selective... 

Heterocycles are of great interest in organic chemistry due to their specific properties. Many of these cycles are widely present in natural and pharmaceutical compounds. Electrochemistry appears as a powerful tool for the preparation and the functionalization of various heterocycles because anodic oxidations and cathodic reductions allow the selective preparation of highly reactive intermediates (radicals, radical ions, cations, anions, and electrophilic and nucleophilic groups). In this way, the electrochemical technique can be used as a key step for the synthesis of complex molecules containing heterocycles. A review of the electrolysis of heterocyclic compounds is summarized in Ref. [1]. 

Electrochemistry is one of the most promising areas in the research of conducting polymers. Thus, the method of choice for preparing conducting polymers, with the exception of PA, is the anodic oxidation of suitable monomeric species such as pyrrole [3], thiophene [4], or aniline [5]. Several aspects of electrosynthesis are of relevance for electrochemists. First, there is the deposition process of the polymers at the electrode surface, which involves nucleation-and-growth steps [6]. Second, to analyze these phenomena correctly, one has to know the mechanism of electropolymerization [7, 8]. And thirdly, there is the problem of the optimization of the mechanical, electrical, and optical material properties produced by the special parameters of electropolymerization. 

Parhutik VP, Makushok IE, Kudriavtsev E, Sokol VA, Khodan AN (1987) An X-ray electronic study of the formation of anodic oxide films on aluminium in nitric acid. Electrochemistry (Elektrokhymia) 23 1538-1544 Kundu M, Khosravi AA, Kulkami SK (1997) Synthesis and study of organically capped ultra small clusters of cadmium sulphide. J Mater Sci 32 245-258... 

The tetraphenylallene system represents a particularly elegant confluence of chemistry, electrochemistry, and EPR. The carbanion of 1,1,3,3-tetraphenyl-propene is formed spontaneously in alkaline medium. Or it can be formed by the two-electron reduction of 2-ethoxy-1,1,3,3-tetrapheny 1-prop- 1-ene (at 2.2 V) or of tetraphenylallene (at -2.11 V). The tetraphenylallyl radical is then produced by anodic oxidation of the carbanion at -0.95 V. Its EPR spectrum was obtained using the two-stage flow cell described earlier [37]. 

This review describes the electrochemical behavior of compounds containing the C=C, C=0 and C=N functional group. The review covers both anodic oxidation and cathodic reduction of such compounds. The electrochemistry of these functionalities was reviewed in an earlier volume of this series1 this article updates the previous one but does not include the material included there. The Kolbe oxidation of carboxylic acids has... 

What, then, is the part of the process that j ustifies the heading of this section and brings the material into a chapter on materials science in electrochemistry It is the process by which xanthates adsorb. It has been established (Nixon, 1957) that the formation of the monolayer of an organic substance is not a physical but a chemical, indeed an electrochemical, process. The xanthate undergoes an anodic oxidation ... 

Oxides are by no means new materials to electrochemists [63-76] and have been actively studied in connection with electrocatalysis and anodic oxidation of metals. In particular, a great deal of information has accumulated on the electrochemistry of two- (and more-) component perovskites and also of spinels, both of which are structurally similar to HTSC oxides. 

An important application of combined electrochemistry and ESR spectroscopy is the characterization and identification of intermediates and products of electrode reactions [334,336,379-391]. For instance, the ESR technique is particularly useful to measure the degree of protonation under conditions where the radical ions take part in acid-base equilibria [380,381]. Such information may be obtained only with difficulty by other methods, but the coupling pattern of the ESR spectrum may often give the answer directly. An illustrative example is found in the anodic oxidation of 2,4,6-tri-rert-butylaniline, which, as expected, gives the radical cation as the initial electrode product [380]. In an aprotic solvent like MeCN or CH3NO2 the radical cation is stable and the ESR spectrum observed is in accordance with the reversible one-electron transfer indicated by CV. However, when the electrolysis is carried out in the presence of diphenylguanidine as a base, the ESR spectrum changes drastically and can be attributed to the presence of the neutral free radical formed by deprotonation of the radical cation. 

The electrochemistry of amino acids has been studied in strong acid solutions. In general, the compounds are decomposed to carboxylic acids, aldehydes, ammonia, and carbon dioxide. The results are reviewed by Weinberg [35]. The anodic oxidation mechanism has been studied in pH 10 buffer solution. Decarboxylation accompanied by C-N bond cleavage is the main reaction process [182]. The synthetically interesting Hofer-Moest decarboxylations of A/ -protected amino acids and a-amino malonic half esters under the formation of A/ -acyliminium ions is treated in the following section. 

The complexity of the system implies that many phenomena are not directly explainable by the basic theories of semiconductor electrochemistry. The basic theories are developed for idealized situations, but the electrode behavior of a specific system is almost always deviated from the idealized situations in many different ways. Also, the complex details of each phenomenon are associated with all the processes at the silicon/electrolyte interface from a macro scale to the atomic scale such that the rich details are lost when simplifications are made in developing theories. Additionally, most theories are developed based on the data that are from a limited domain in the multidimensional space of numerous variables. As a result, in general such theories are valid only within this domain of the variable space but are inconsistent with the data outside this domain. In fact, the specific theories developed by different research groups on the various phenomena of silicon electrodes are often inconsistent with each other. In this respect, this book had the opportunity to have the space and scope to assemble the data and to review the discrete theories in a global perspective. In a number of cases, this exercise resulted in more complete physical schemes for the mechanisms of the electrode phenomena, such as current oscillation, growth of anodic oxide, anisotropic etching, and formation of porous silicon. 

The basic electrochemistry of the substrate is an important ingredient in the anodic oxidation process. The ease of doing the oxidation will definitely determine the material to be chosen for making the pattern. It appears that the two most popular substances which have been studied and used most extensively are Ti (for formation of TiO ) and H-passivated Si (for formation of Si02). 

Similar efforts in solid-state electrochemistry for SOFC development focus on the exploration of new perovskites not only for the ORR but also for the anodic oxidation of hydrocarbons [182]. In this area, the discovery that Cu-based anodes present a viable alternative to the classical Ni-YSZ cermet anodes is particularly noteworthy [166, 183, 184], owing to the significant enhancement of performance by avoiding coke deposition. Similar important advances have occurred in the molten carbonate fuel cell (MCFC) area [9]. 

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