Electrode clusters

The experimental data and arguments by Trassatti [25] show that at the PZC, the water dipole contribution to the potential drop across the interface is relatively small, varying from about 0 V for An to about 0.2 V for In and Cd. For transition metals, values as high as 0.4 V are suggested. The basic idea of water clusters on the electrode surface dissociating as the electric field is increased has also been supported by in situ Fourier transfomr infrared (FTIR) studies [26], and this model also underlies more recent statistical mechanical studies [27]. 

In the discussion of the relative acidity of carboxylic acids in Chapter 1, the thermodynamic acidity, expressed as the acid dissociation constant, was taken as the measure of acidity. It is straightforward to determine dissociation constants of such adds in aqueous solution by measurement of the titration curve with a pH-sensitive electrode (pH meter). Determination of the acidity of carbon acids is more difficult. Because most are very weak acids, very strong bases are required to cause deprotonation. Water and alcohols are far more acidic than most hydrocarbons and are unsuitable solvents for generation of hydrocarbon anions. Any strong base will deprotonate the solvent rather than the hydrocarbon. For synthetic purposes, aprotic solvents such as ether, tetrahydrofuran (THF), and dimethoxyethane (DME) are used, but for equilibrium measurements solvents that promote dissociation of ion pairs and ion clusters are preferred. Weakly acidic solvents such as DMSO and cyclohexylamine are used in the preparation of strongly basic carbanions. The high polarity and cation-solvating ability of DMSO facilitate dissociation... 

The Hg/V-methylformamide (NMF) interface has been studied by the capacitance method as a function of temperature.108,294,303 The potential of Hg was measured with respect to the reference electrode Ag/0.05 M AgC104 + 0.05 M NaC104 in water. The specific adsorption of C104 was found to be negligible at a < 6 /iC cm"2. The experimental capacitance data have been discussed in terms of the four-state model,121,291,294 which assumes the presence of both monomers and clusters in the surface layer of the solvent. The model has been found to describe the experimental picture qualitatively but not quantitatively. This is related to the fact that NMF is a strongly associated solvent.108,109,294,303... 

Good agreement between C(- and the dipole moment of the solvent (H20) molecules (i.e., by the hydrophilicity of metals) established by Trasatti25,31 was found and the reasons for this phenomenon were explained 428 The Valette and Hamelin data150 251 387-391 are in agreement with the data from quantum-chemical calculations of water adsorption at metal clusters 436-439 where for fee metals it was found that the electrode-H20 interaction increases as the interfacial density of atoms decreases. 

Quantum mechanical calculations electrochemical promotion, 267 with copper clusters, 268 with platinum clusters, 268 Quasi-reference electrodes, 118... 

When Rutherford allowed the radiation to pass between two electrically charged electrodes, he found that one type was attracted to the negatively charged electrode. He proposed that the radiation attracted to the negative electrode consists of positively charged particles, which he called a particles. From the charge and mass of the particles, he was able to identify them as helium atoms that had lost their two electrons. Once Rutherford had identified the atomic nucleus (in 1908, Section B), he realized that an a particle must be a helium nucleus, He2+. An a particle is denoted or simply a. We can think of it as a tightly bound cluster of two protons and two neutrons (Fig. 17.5). 

The redox properties of a series of heterometal clusters were assessed by electrochemical and FPR measurements. The redox potentials of derivatives formed in D. gigas Fdll were measured by direct square wave voltammetry promoted by Mg(II) at a vitreous carbon electrode, and the following values were determined 495, 420,... 

A somewhat similar approach has been nsed for the formation of nanosize wires stretching between gold electrodes [34]. Lambda-DNA was positioned between two electrodes, with immobilized oligonncleotides complementary to lambda-DNA sticky ends. Silver (Ag ) ions were deposited on the stretched DNA bridges, followed by rednction of absorbed ions to metallic silver with hydroquinone. The resulting silver clusters formed on DNA strands were found to be 100 nm in diameter and were capable of condncting the electric current. 

Perspectives for fabrication of improved oxygen electrodes at a low cost have been offered by non-noble, transition metal catalysts, although their intrinsic catalytic activity and stability are lower in comparison with those of Pt and Pt-alloys. The vast majority of these materials comprise (1) macrocyclic metal transition complexes of the N4-type having Fe or Co as the central metal ion, i.e., porphyrins, phthalocyanines, and tetraazaannulenes [6-8] (2) transition metal carbides, nitrides, and oxides (e.g., FeCjc, TaOjcNy, MnOx) and (3) transition metal chalcogenide cluster compounds based on Chevrel phases, and Ru-based cluster/amorphous systems that contain chalcogen elements, mostly selenium. 

Electric Breakdown in Anodic Oxide Films Physics and Applications of Semiconductor Electrodes Covered with Metal Clusters Analysis of the Capacitance of the Metal-Solution Interface. Role of the Metal and the Metal-Solvent Coupling Automated Methods of Corrosion Measurement... 

Interfacial water molecules play important roles in many physical, chemical and biological processes. A molecular-level understanding of the structural arrangement of water molecules at electrode/electrolyte solution interfaces is one of the most important issues in electrochemistry. The presence of oriented water molecules, induced by interactions between water dipoles and electrode and by the strong electric field within the double layer has been proposed [39-41]. It has also been proposed that water molecules are present at electrode surfaces in the form of clusters [42, 43]. Despite the numerous studies on the structure of water at metal electrode surfaces using various techniques such as surface enhanced Raman spectroscopy [44, 45], surface infrared spectroscopy [46, 47[, surface enhanced infrared spectroscopy [7, 8] and X-ray diffraction [48, 49[, the exact nature of the structure of water at an electrode/solution interface is still not fully understood. 

Matsushita, M Hayakawa, Y. and Sawada, Y. (1985) Fractal structure and cluster statistics of zinc-metal trees deposited on a line electrode. Phys. Rev. A, 32, 3814-3816. 

The redox potentials of the ITO electrodes modified with CgoN -MePH clusters were measured by cyclic voltammetry and differential pulse voltammetry in the absence and presence of magnetic processing. 

The photoelectrochemical properties of ITO electrodes modified with CeoN -MePH clusters were also measured in the presence and absence of magnetic... 

Figure 15.6 Effects of magnetic processing on (a) DPV curves (b) potential dependences of photocurrents of QqN " -MePH clusters on ITO electrodes.

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