Materials electroactive

Electrode processes are a class of heterogeneous chemical reaction that involves the transfer of charge across the interface between a solid and an adjacent solution phase, either in equilibrium or under partial or total kinetic control. A simple type of electrode reaction involves electron transfer between an inert metal electrode and an ion or molecule in solution. Oxidation of an electroactive species corresponds to the transfer of electrons from the solution phase to the electrode (anodic), whereas electron transfer in the opposite direction results in the reduction of the species (cathodic). Electron transfer is only possible when the electroactive material is within molecular distances of the electrode surface thus for a simple electrode reaction involving solution species of the fonn... 

Pick s second law of difflision enables predictions of concentration changes of electroactive material close to the electrode surface and solutions, with initial and boundary conditions appropriate to a particular experiment, provide the basis of the theory of instrumental methods such as, for example, potential-step and cyclic voltanunetry. 

The anode may be operated in the temperature range — 18 C to 65 C and at currents up to 0 05 A per linear metre in soil and O-Ol A per linear metre in water, which corresponds with an effective maximum current densities of 0-66 Am in soil and 0-13 Am in water. No precise details on the anode consumption rate have been provided by the manufacturer, but since the electroactive material is carbon the consumption rate would be expected to be of a similar order to that exhibited by graphite anodes. 

At the electrode surface there is competition among many reduction reactions, the rates of which depend on iQ and overpotential q for each process. Both /0 and q depend on the concentration of the electroactive materials (and on the catalytic properties of the carbon surface). However, the chemical composition of the SEI is also influenced by the solubility of the reduction products. As a result, the voltage at... 

The SEI is formed by parallel and competing reduction reactions and its composition thus depends on i0, t], and the concentrations of each of the electroactive materials. For carbon anodes, (0 also depends on the surface properties of the electrode (ash content, surface chemistry, and surface morphology). Thus, SEI composition on the basal plane is different from that on the cross—section planes. 

Comparison of Properties of Dielectric Elastomers with Other Electroactive Materials... 

Sodium valproate has been determined in pharmaceuticals using a valproate selective electrode [13,14]. The electroactive material was a valproate-methyl-tris (tetra-decyl)ammonium ion-pair complex in decanol. Silver-silver chloride electrode was used as the reference electrode. The electrode life span was >1 month. Determination of 90-1500 pg/mL in aqueous solution by direct potentiometry gave an average recovery of 100.0% and a response time of 1 min. 

Support by the Austrian Science Funds through the special research program "Electroactive Materials" is gratefully acknowledged. 

Torre G, Nicolau M, Torres T (2001) In Nalwa HS (ed) Supramolecular photosensitive and electroactive materials. Academic, New York, p 1... 

In this section, we look more closely at what effect the chalcogen atom has on the properties of the molecular conductors we describe. We do not attempt to review exhaustively all the chalcogen-containing components in electroactive systems, to do so would be a colossal task. Instead, carefully chosen examples and studies illustrate how chalcogen chemistry is used in the design and manipulation of electroactive materials, and ultimately how it effects suitability for molecular device applications. 

Short intramolecular contacts between chalcogens and other chalcogens or other heteroatoms have been shown to influence molecular geometry, particularly planarity, in many structures of electroactive materials. Hence the position of the chalcogen atom in the material can profoundly affect its properties. For example Crouch et al 2 report the X-ray crystal structure of compound 24 (Figure 10), a candidate for an organic field-effect transistor, showing the effect of intramolecular S- F close contacts (in tandem with H F contacts) on the planarity of the molecule in the solid state. Note also the... 

Chemical Sensors A Case Study of Chalcogen-Metal Bonding in Electroactive Materials... 

A concentration cell contains the same electroactive material in both half-cells, but in different concentration (strictly, with different activities). The emf forms in response to differences in chemical potential /r between the two half-cells. Note that such a concentration cell does not usually involve different electrode reactions (other than, of course, that shorting causes one half-cell to undergo reduction while the other undergoes oxidation). 

See also Carbon monoxide (CO) Copolyamides, random, 19 762-763 Copoly(disulfide)s, as electroactive materials, 23 713—714 Copolyestercarbonates, 19 822 Copolyester elastomers, thermoplastic, 20 70-71... 

Potentiometric Determination of Lead (II) Ion using 2-[(4-Chloro-Phenylimino)-Methyl]-Phenol as an electroactive Material... 

In contrast, in galvanostatic exhaustive electrolysis the current through the working electrode is kept constant. As in chronopo-tentiometry, this will result in a constant flux of electroactive material to the surface. Consequently, the electrode potential will vary during the experiment. As a result, at different times various electrode processes may be induced. Hence, the results of galvanostatic and potentiostatic electrolyses will not necessarily be identical. 

The electron formed as a product of equation (2.5) will usually be received (or collected ) by an electrode. It is quite common to see the electrode described as a sink of electrons. We need to note, though, that there are two classes of electron-transfer reaction we could have considered. We say that a reaction is heterogeneous when the electroactive material is in solution and is electro-modified at an electrode which exists as a separate phase (it is usually a solid). Conversely, if the electron-transfer reaction occurs between two species, both of which are in solution, as occurs during a potentiometric titration (see Chapter 4), then we say that the electron-transfer reaction is homogeneous. It is not possible to measure the current during a homogeneous reaction since no electrode is involved. The vast majority of examples studied here will, by necessity, involve a heterogeneous electron transfer, usually at a solid electrode. 

In order to avoid all possible ambiguity, we will not use the word reduce again in this text to mean either decrease or get smaller, but will only use it to mean that an electroactive material has acquired electrons. 

During reduction, electrons travel/rom the power pack, through the electrode, transfer across the electrode-solution interface and enter into the electroactive species in solution. Conversely, during oxidation, electrons move in the opposite direction, and are conducted away from the electroactive material in solution and across the electrode-solution interface as soon as the electron-transfer reaction occurs. (Incidentally, these different directions of electron movement explains why an oxidative current has the opposite sign to a reductive current, cf. Section 1.2.)... 

If the movement of an electron is this fast, we see that the overall rate of charge movement will depend either on the rate at which the electroactive material... 

Electroanalyte movement through solution. If electron conduction through the electrode and electron transfer across the interface are both fast, then the rate that limits the overall rate of charge flow will be that at which the electroactive material moves from the solution to approach close enough to the electrode for electron transfer to occur. 

Convection. This is the physical movement of the solution in which the electroactive material is dissolved. In practice, convection arises from two causes, i.e. from deliberate movement of the solution, e.g. by mechanical stirring (sometimes called hydrodynamic control, see Chapter 7) or, alternatively, convection is induced when the amount of charge passed through an electrode causes localized heating of the solution in contact with it. The convective stirring in such instances occurs since the density p of most solvents depends on their temperature typically, p increases as the temperature decreases. 

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. 

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