Electroactive, defined

Moreover, under well-defined experimental conditions, the organic anion produced may be unstable and undergo isomerisation or/and elimination. Several examples of side-reactions or unexpected formation of new electroactive species at the cathodic interface are listed in the following subsections. 

The polymer-solvent interaction parameter, which is a key constant defining the physical chemistry of every polymer in a solvent, can be obtained from electrochemical experiments. Definition and inclusion of this interaction was a milestone in the development of polymer science at the beginning of the 1950s. We hope that Eq. 47 will have similar influence in the development of all the cross-interactions of electrochemistry and polymer science by the use of the ESCR model. A second point is that Eq. 47 provides us with an efficient tool to obtain this constant in electroactive... 

Since model compounds reveal well-defined cyclic voltammograms for the Cr(CNR)g and Ni(CNR)g complexes (21) the origin of the electroinactivity of the polymers is not obvious. A possible explanation (12) is that the ohmic resistance across the interface between the electrode and polymer, due to the absence of ions within the polymer, renders the potentially electroactive groups electrochemically inert, assuming the absence of an electronic conduction path. It is also important to consider that the nature of the electrode surface may influence the type of polymer film obtained. A recent observation which bears on these points is that when one starts with the chromium polymer in the [Cr(CN-[P])6] + state, an electroactive polymer film may be obtained on a glassy carbon electrode. This will constitute the subject of a future paper. 

Figure 5.37 depicts the stationary distribution of the electroactive substance (the reaction layer) for kc—> oo. The thickness of the reaction layer is defined in an analogous way as the effective diffusion layer thickness (Fig. 2.12). It equals the distance [i of the intersection of the tangent drawn to the concentration curve in the point x = 0 with the line c = cA/K,...

They found that the hydrolysis products of 4-AP and 1-naphthol produced well-defined anodic responses at low potentials at a bare SPCE. However, the presence of antibody immobilized on the electrode surface slowed the diffusion of 4-AP towards the electrode surface. In addition, 4-AP may interact with polyphenols on the electrode surface, thus reducing the electroactive working area of the electrode by fouling. In contrast, diffusion of 1-naphthol to the electrode surface was not hindered by immobilized antibody. This feature, along with its low cost, ease of availability, and high solubility, resulted in 1-NP being the preferred AP substrate in their work. 

Another problem that is common for all membrane-based solid-state sensors is the ill-defined membrane-metal interface. A large exchange current density is required to produce a reversible interface for a stable potentiometric sensor response. One approach to improving this interface is to use conducting polymers. Conducting polymers are electroactive n-conjugated polymers with mixed ionic and electronic conductivity. They... 

One can define as outer-sphere electrode processes those in which the electron transfer between the electrode and the active site occurs through the layer of solvent directly in contact with the electrode surface. The electrode and electroactive species are, therefore, separated such that the chemical interaction between them can be considered practically nil (obviously, apart from their electrostatic interaction), see Figure 1. 

Inner-sphere electrode processes are defined as those in which the electron exchange occurs between the electrode and the electroactive species (the metal core or its ligand) that are in direct contact with the electrode surface, see Figure 2. 

Diffusion. Often, the most important mode of mass transport is diffusion. The rate of diffusion can be defined in terms of Pick s laws. These two laws are framed in terms of flux, that is, the amount of material impinging on the electrode s surface per unit time. Pick s first law states that the flux of electroactive material is in direct proportion to the change in concentration c of species i as a function of the distance x away from the electrode surface. Pick s first law therefore equates the flux of electroanalyte with the steepness of the concentration gradient of electroanalyte around the electrode. Such a concentration gradient will always form in any electrochemical process having a non-zero current it forms because some of the electroactive species is consumed and product is formed at the same time as current flow. 

The existence of a maximum thickness beyond which the performance deteriorates is due to the concerted impact of oxygen and proton transport limitations. Considered separately, each of these limitations would only serve to define a minimum thickness below which performance worsens due to an insufficient electroactive surface. The thickness of the effective layer, in which current density is predominantly generated, is given by the reaction penetration depth ... 

The charging process implies the oxidation of the cathode polymer with the concurrent insertion of the C104 anions from the electrolyte and the deposition of lithium at the anode. In the discharging process the electroactive cathode material releases the anion and the lithium ions are stripped from the metal anode to restore the initial electrolyte concentration. Therefore, the electrochemical process involves the participation of the electrolyte salt to an extent which is defined by the doping level y. 

The synthetic procedure to create the dibenzo[l,2]dithiin derivative 237 (Scheme 67) with a well-defined chromo-phore and also electroactive under mild conditions has been published <2006TL9135> the disulfide bridge proved electrochemically switchable. 

The attention devoted to supramolecular sensitizers containing multifold chromophoric and electroactive centers arises from the construction of molecular devices based on nanometric and well-defined molecular architectures [4]. The use of these species for sensitization of titanium dioxide has provided fundamental insights into interfacial electron-transfer processes. 

Voltammetry has been adapted to HPLC (when the mobile phase is conducting) and capillary electrophoresis (CE) as a detection technique for electroactive compounds. In this usage, the voltammetric cell has to be miniaturised (to about 1 pi) in order not to dilute the analytes after separation. A metal or carbon microelectrode has a defined potential (vs the reference electrode) depending on the substances to be detected (ions or molecules) and the mobile phase flows through the detection cell (Fig. 19.5). This method of amperometric detection in the pulsed mode is very... 

We are now in a position to examine, in quantitative detail, the effect of the supporting electrolyte, at least for steady-state homovalent transport in finite planar geometry. The amount of supporting electrolyte present, relative to electroactive electrolyte, is characterized by the support ratio that was defined as... 

An operational definition of thin-layer electrochemistry is that area of electrochemical endeavor in which special advantage is taken of restricting the diffii-sional field of electroactive species and products. Typically, the solution under study is confined to a well-defined layer, less than 0.2 mm thick, trapped between an electrode and an inert barrier, between two electrodes, or between two inert barriers with an electrode between. Diffusion under this restricted condition has been described in Chapter 2 (Sec. II.C). Solution trapped in a porous-bed electrode will have qualitatively similar electrochemical properties however, geometric complexities make this configuration less useful for analytical purposes. The variety of electrical excitation signals applicable to thin-layer electrochemical work is large. Three reviews of the subject have appeared [28-30]. 

Voltammetry experiments are occasionally undertaken in the form of a tubular or rectangular channel through which the electrolyte solution is pumped at a more or less constant velocity. The electrode may form the channel itself or be embedded in the wall of an inert material, which defines the flow pattern. Sometimes the channel is packed with small particles of electrode material in contact with each other. The latter situation is designed to improve the conversion efficiency of the cell. When all the electroactive molecules are converted during passage through such a porous bed, the efficiency is 100% and the cell is said to be operating coulometrically (see Sec. IV.F). 

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