Electrochemically active chemical

Water is an electrochemically active chemical species. The electrochemical reactions in which water is the primary reactant or product are... 

Electrochemistry provides a powerful tool for elucidating the pH-dependent redox mechanisms of coordination complexes. In principle, any electrochemically active chemical (or biological) system may exhibit pH-dependent reduction potentials, if the concomitant pH-dependent process occurs on the same timescale as electron transfer. While the pH-dependent process is ultimately chemical in nature (i.e., involves bond breaking and/or bond making), the phenomenon that perturbs the redox center and alters the reduction potential may be electronic, structural (e.g., a conformational change), or environmental (e.g., changes in solvation), and often will be some ill-defined combination of these factors. ... 

Electrochemical measurements are commonly carried out in a medium that consists of solvent containing a supporting electrolyte. The choice of the solvent is dictated primarily by the solubility of the analyte and its redox activity, and by solvent properties such as the electrical conductivity, electrochemical activity, and chemical reactivity. The solvent should not react with the analyte (or products) and should not undergo electrochemical reactions over a wide potential range. 

Other methods have been developed for the removal of oxygen (particularly from flowing streams). These include the use of electrochemical or chemical (zinc) scrubbers, nitrogen-activated nebulizers, and chemical reduction (by addition of sodium sulfite or ascorbic acid). Alternately, it may be useful to employ voltam-... 

This reduction step can be readily observed at a mercury electrode in an aprotic solvent or even in aqueous medium at an electrode covered with a suitable surfactant. However, in the absence of a surface-active substance, nitrobenzene is reduced in aqueous media in a four-electron wave, as the first step (Eq. 5.9.3) is followed by fast electrochemical and chemical reactions yielding phenylhydroxylamine. At even more negative potentials phenylhydroxylamine is further reduced to aniline. The same process occurs at lead and zinc electrodes, where phenylhydroxylamine can even be oxidized to yield nitrobenzene again. At electrodes such as platinum, nickel or iron, where chemisorption bonds can be formed with the products of the... 

Reaction of [Ir(Me)2cp (L)], L = PPh3, PMePh2, PMe2Ph, PMe3, with NOBF4 in CH2C12 affords [Ir(Me)2cp (NO)]BF4 and [Ir(Me)cp (NO)L](BF4)2, (71).95 EPR spectroscopy shows that the reaction proceeds through the IrlV intermediate. Electrochemical or chemical reduction of (71) yields the EPR-active species [Ir(Me)cp (NO)L](BF4), in which the unpaired electron is partially delocalized on the Ir nucleus. 

These differences in film morphology were also reflected as differences in film formation conditions, film adhesion, and in electrochemical properties. The pyrazoline beads readily formed films from solvents such as benzene. For the phenoxy TTF system, however, only CH2Cl2 was effective in forming films. In general, the TTF cross-linked polymers were found to be less adherent to the metallized substrates than the pyrazoline cross-linked polymers. Electro-chemically, it was found that the pyrazoline films showed complete activity after one potential sweep. The TTF polymer films, on the other hand, required from 5 to 20 cycles to reach full electrochemical activity as evidenced by a constant voltammogram with cycling. Furthermore, it was observed that the TTF polymer films were much less electroactive than the pyrazoline materials as shown by optical densities and total coulombs passed which were several times less for the TTF systems. 

A Chemical Reaction Interposed Between Two Electron Transfers. An electrochemical process in which the product of the electron transfer undergoes a chemical reaction that generates a species which in turn is electrochemically active is defined as an ECE mechanism. It is commonly schematized as ... 

In this chapter, two carbon-supported PtSn catalysts with core-shell nanostructure were designed and prepared to explore the effect of the nanostructure of PtSn nanoparticles on the performance of ethanol electro-oxidation. The physical (XRD, TEM, EDX, XPS) characterization was carried out to clarify the microstructure, the composition, and the chemical environment of nanoparticles. The electrochemical characterization, including cyclic voltammetry, chronoamperometry, of the two PtSn/C catalysts was conducted to characterize the electrochemical activities to ethanol oxidation. Finally, the performances of DEFCs with PtSn/C anode catalysts were tested. The microstmc-ture and composition of PtSn catalysts were correlated with their performance for ethanol electrooxidation. 

Activation Polarization Activation polarization is present when the rate of an electrochemical reaction at an electrode surface is controlled by sluggish electrode kinetics. In other words, activation polarization is directly related to the rates of electrochemical reactions. There is a close similarity between electrochemical and chemical reactions in that both involve an activation barrier that must be overcome by the reacting species. In the case of an electrochemical reaction with riact> 50-100 mV, rjact is described by the general form of the Tafel equation (see Section 2.2.4) ... 

The use of porous membranes as templates for electrode structures was pioneered by Martin and coworkers nearly 20 years ago, and this approach has since been extended to include numerous electrode compositions and geometries " and applications beyond energy storage, including sensing and separations. In this approach, chemical and electrochemical routes are used to fill in the cylindrical, uniform, unidirectional pores of a free-standing membrane with electrochemically active materials and... 

The CoTAA catalysts obtained by the three activation methods show different electrochemical behavior. This appears particularly clearly in the triangular voltage diagrams obtained under inert gas. The curve for chemically activated CoTAA (Fig. 27) is similar to the constant zero curve of electrochemically activated... 

From the very good activity of thermally or electrochemically activated CoTAA for the reaction of CO one might deduce that the oxidation of formic or oxalic acid proceeds, not directly, but by way of a preliminary decarbonylization reaction. However, there is no evolution of gas from CoTAA in a solution of formic acid in dilute sulfuric acid, even at 70 °C. Such a reaction would have to occur on chemical decomposition of formic acid, with evolution of CO and H2O, or CO2 and H2. It may thus be assumed that formic acid is oxidized directly. 

Fig. 7.110. Schematic model for the active surface of the perovskite, in which transition metal B is electrochemically active. (Reprinted with permission from J. O M. Bockris and T. Ottagawa, J. Phys. Chem. 87 2964, copyright 1983 American Chemical Society.)...

There are numerous applications that depend on chemically reacting flow in a channel, many of which can be represented accurately using boundary-layer approximations. One important set of applications is chemical vapor deposition in a channel reactor (e.g., Figs. 1.5, 5.1, or 5.6), where both gas-phase and surface chemistry are usually important. Fuel cells often have channels that distribute the fuel and air to the electrochemically active surfaces (e.g., Fig. 1.6). While the flow rates and channel dimensions may be sufficiently small to justify plug-flow models, large systems may require boundary-layer models to represent spatial variations across the channel width. A great variety of catalyst systems use... 

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