Electrochemically Important Properties

Carbon materials have been widely utilised in both analytical and industrial electrochemistry, where in many areas they have out-performed the traditional noble metals. This diversity and success stems largely from carbons structural polymorphism, chemical stability, low cost, wide potential windows, relatively inert electrochemistry, rich surface chemistry and electro-catalytic activities for a variety of redox reactions [30, 68]. 

As highlighted above, graphene holds inimitable properties that are superior in comparison to other carbon allotropes of various dimensions and from any other electrode material for that matter, thus theoretically suggesting that graphene is an ideal electrode material that could potentially yield significant benefits in many electrochemical applications it is this we explore in greater detail in subsequent chapters. 

Fitzer, K.-H. Kochling, H.-P. Boehm, H. Marsh, Pure Appl. Chem. 67, 473-506 (1995) 

Web-Resource, The 2010 nobel prize in physics—press release, Nobelprize.org. http //www. nobelprize.org/nobel prizes/physics/laureates/2010/press.html. Accessed 28 Feb 2012 

Clauss, G.O. Fischer, U. Hofmann, Z. Naturforsch. B Anorg. Chem. Org. Chem. Biochem. Biophys. Biol. 17, 150-153 (1962) 

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The natural corrosion resistance of zinc is, therefore, its most important property in relation to zinc coatings. The electrochemical property becomes important when the zinc coating is damaged in any way to expose the steel, when sacrificial corrosion of the zinc occurs and the steel is thereby protected. Moreover, the corrosion product of the zinc normally fills the break in the coating and prevents or retards further corrosion of the exposed steel. 

It will also be shown that the absolute electrode potential is not a property of the electrode but is a property of the electrolyte, aqueous or solid, and of the gaseous composition. It expresses the energy of solvation of an electron at the Fermi level of the electrolyte. As such it is a very important property of the electrolyte or mixed conductor. Since several solid electrolytes or mixed conductors based on ZrC>2, CeC>2 or TiC>2 are used as conventional catalyst supports in commercial dispersed catalysts, it follows that the concept of absolute potential is a very important one not only for further enhancing and quantifying our understanding of electrochemical promotion (NEMCA) but also for understanding the effect of metal-support interaction on commercial supported catalysts. 

Catalytic activity and electrochemical performance generally increase as the NiO and YSZ particle sizes are reduced. However, ultrafine powders are prone to agglomeration during the milling and mixing process the distributions of the phases (and hence the percolation threshold and many other important properties) are determined by the agglomeration size, not by the primary particle size. 

A particular important property of silicon electrodes (semiconductors in general) is the sensitivity of the rate of electrochemical reactions to the radius of curvature of the surface. Since an electric field is present in the space charge layer near the surface of a semiconductor, the vector of the field varies with the radius of surface curvature. The surface concentration of charge carriers and the rate of carrier supply, which are determined by the field vector, are thus affected by surface curvature. The situation is different on a metal surface. There exists no such a field inside the metal near the surface and all sites on a metal surface, whether it is curved not, is identical in this aspect. 

Early in the last century, Paul Sabatier1 pointed out A most important property of an excellent catalyst is that it has an ability to bind many molecules but not too strongly . This Sabatier s principle is also the principle for how an excellent catalyst for electrochemical reactions works. In electrochemical terms, an active... 

When a non-aqueous solvent is to be used for a given purpose, a suitable one must be selected from the infinite number available. This is not easy, however, unless there are suitable guidelines available on how to select solvents. In order to make solvent selection easier, it is useful to classify solvents according to their properties. The properties of solvents and solvent dassification have been dealt with in detail in the literature [1, 2]. In this chapter, these problems are briefly discussed in Sections 1.1 and 1.2, and then the influences of solvent properties on reactions of electrochemical importance are outlined in Section 1.3. 

Tab. 1.1 Physical properties of organic solvents and some inorganic solvents of electrochemical importance... 

It has been necessary to understand the relationship between molecular fine structure of cyanine dyes and important properties such as colour, dye aggregation, adsorption on silver halide and electrochemical potentials in order to design and prepare sensitizers with optimum performance. For general discussion of these topics and the mechanism of spectral sensitization, the reader is referred to recent surveys on the subject (B-77MI11401, 77HC(30)441). 

The Physicochemical Properties of Solvents and Their Relevance to Electrochemistry. The solvent properties of electrochemical importance include the following protic character (acid-base properties), anodic and cathodic voltage limits (related to redox properties and protic character), mutual solubility of the solute and solvent, and physicochemical properties of the solvent (dielectric constant and polarity, donor or solvating properties, liquid range, viscosity, and spectroscopic properties). Practical factors also enter into the choice and include the availability and cost of the solvent, ease of purification, toxicity, and general ease of handling. 

ILs are defined as organic salts having a melting point (Tm) below 100°C [1-5]. In order to use these ILs as non-volatile electrolyte solutions, it is necessary to maintain the liquid phase over a wide temperature range. Consequently, Tm and the thermal degradation temperature (Tfj of ILs are important properties for ILs as electrochemical media. In this section, the thermal properties of ILs, especially of imidazolium salts, are summarized. The difference between ILs and general electrolyte solutions based on molecular solvents is clarified. Recent results on the correlation between the structure and properties of ILs will also be mentioned. 

The thermal conductivity of ILs is an important property when using ILs for electrochemical synthesis or thermal storage. The thermal conductivity of ILs was reported, together with heat capacity, by Wilkes et al., as summarized in Table 3.4 [44]. The heat capacities of I Ls are 3 or 4 times larger than that of copper, but smaller than that of water. The thermal conductivity of general ILs is lower than that of copper or water. Therminol VP-1, diphenyl oxide/biphenyl type thermal conductor, is commercially available as a heat transport fluid. The thermal conductivity and heat capacity of ILs are, in general, similar to those of VP-1. 

One of the most important properties of all solvents used for electrochemical studies is the available potential range or the electrochemical window. The electrochemical window is the range of potentials across which it is possible to observe an electrochemical reaction of a substance dissolved in a solvent. Each... 

The anions mentioned in the previous section have been extensively investigated to make clear their electrochemical properties, such as stability, ionic conductivities, transference numbers, impurities, and so on. The most important property among... 

A second important property of Eq. (149) is that it provides an estimate of the rate, in terms of a characteristic time 6, associated with mass transfer. Indeed, this is the time 9 needed for a molecule to reach the electrode, that is, to cover the space interval in which the molecular concentration differs from that in the bulk. In transient methods this time is identical to that elapsed since the beginning of the experiment, provided that it is lower than tmax = conv/2D. For steady-state methods, the length to be covered is (Sconv and thus from Eq. (149) it follows that 9 = 5conv/2D. The rate of mass transfer can be defined as 1 /9, since it is obviously equivalent to a first-order process (see Chapter 3 for a demonstration of this point). Yet in light of the previous discussion, it is preferable to think in terms of a characteristic time 9 associated with a given electrochemical method rather than in terms of mass transfer rate, although this intuitive latter notion was extremely worthwhile up to this point. ... 

Carbon (C)-aerogels have been investigated for one decade as a promising material for electrochemical applications in supercapacitors, fuel cells and waste water treatment [1,2], C-aerogels are nanoporous, electrically conducting and monolithic materials that provide the unique possibility to tailor the carbon properties on a molecular scale. The surface area and the degree of microporosity can be adjusted almost independently of the overall porosity for which mainly meso- and macropores are responsible. Whereas the mesostructure is determined by the stoichiometry of the reactants in the precursor solution, the pyrolysis conditions control the micropore structure of the material [3,4]. High pyrolysis temperatures will increase the electrical conduchvity [5], an important property for many electrochemical applications. 

A particularly important property of silicon electrodes is the sensitivity of the rate of electrochemical reactions to the radius of curvature of the surface, i.e., the sensitiv-... 

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