Electrochemical devices development

Electrodes modified with phthalocyanines show interesting sensing properties due to their rich electrocatalytic behavior, whose properties can be tuned by the introduction of different substituents. In this section we will discuss only those electrochemical devices developed to detect quantitatively organic compounds similar to those whose degradation has been addressed in the first part of this chapter. 

Starting in the 1950s, electrochemical principles have been employed in the development of new technical means for the acquisihon, measurement, storage, transformation, and transfer of various types of informahon. By now many electrochemical devices have been developed for such purposes and are used to build automated systems for the control of production processes, for the automation of geophysical observations and measurements, and for many other purposes. This field, intermediate between electrochemistry, informatics, and electronics, is also known as chemotronics. 

Studies of photoelectrochemical phenomena are of great theoretical value. With light as an additional energy factor, in particular, studies of the elementary act of electrochemical reactions are expedited. Photoelectrochemical phenomena are of great practical value as well. One of the most important research activities nowadays is development of electrochemical devices for a direct conversion of luminous (solar) into electrical energy and photoelectrochemical production of hydrogen. 

The goal of this book is to cover the full scope of electrochemical sensors and biosensors. It offers a survey of the principles, design and biomedical applications of the most popular types of electrochemical devices in use today. The book is aimed at all scientists and engineers who are interested in developing and using chemical sensors and biosensors. By discussing recent advances, it is hoped to bridge the common gap between research literature and standard textbooks. 

The desire to realise technological goals has spurred the discovery of many new solid electrolytes and intercalation compounds based on crystalline and amorphous inorganic solids. In addition an entirely new class of ionic conductors has been discovered by P. V. Wright (1973) and M. B. Armand, J. M. Chabagno and M. Duclot (1978). These polymer electrolytes can be fabricated as soft films of only a few microns, and their flexibility permits interfaces with solid electrodes to be formed which remain intact when the cells are charged and discharged. This makes possible the development of all-solid-state electrochemical devices. 

More recently, Ingram et al. and Wright et al. independently tried to develop new polymer hosts with secondary structures similar to that of a liquid crystalline state, so that ion transport could occur with a higher degree of freedom in the highly oriented environments and become at least partially decoupled from the polymer segmental relaxations. Ion conductivities approaching liquidlike values have been obtained on the condition that the liquid crystalline state could be maintained. However, the incorporation of these novel polymer materials in electrochemical devices remains to be tested. 

The development of solid state conducting solids that are on a par with liquid electrolytes has revolutionized the design of batteries and other solid state ionic devices (SSIs) in recent years, and this section explains the operating principles behind some of these devices. Figure 5.15 is a simple schematic diagram which we can use to explain the operation of several different types of electrochemical device. 

In recent years, considerable effort has gone into the development of a new class of electrochemical devices called chemically modified electrodes. While conventional electrodes are typified by generally nonspecific electrochemical behavior, i.e., they serve primarily as sites for heterogeneous electron transfer, the redox (reduction-oxidation) characteristics of chemically modified electrodes may be tailored to enhance desired redox processes over others. Thus, the chemical modification of an electrode surface can lead to a wide variety of effects including the retardation or acceleration of electrochemical reaction rates, protection of electrodes, electro-optical phenomena, and enhancement of electroanalytical specificity and sensitivity. As a result of the importance of these effects, a relatively new field of research has developed in which the... 

Sagitova, F Bejan, D Bunce, N.J. and Miziolek, R. (2005) Development of an electrochemical device for removal of arsenic from drinking water. Canadian Journal of Chemical Engineering, 83(5), 889-95. 

An electrochemical flow detector, based on four working electrodes coated with different permselective film types, for use in flow-injection measurements of multiple nitroaromatic explosives was recently developed [18]. The resulting array response (Fig. 4) offers unique fingerprints of such explosive compounds. Electrochemical devices are extremely attractive for designing such e-nose-type multi-electrode arrays that combine several partially selective electrodes and lead to a distinct response pattern (signature) for mixtures of organic vapors without prior separation [2],... 

In the applications described so far, catalytic data were not acquired along with the spectroscopic data, or the cells were unsuitable for correct measurements of the former. The determination of the catalyst structure and performance in a single experiment is not only of interest for catalysts but for any functional material. For instance, rather similar developments as in the field of catalysis have been reported in the fields of gas sensors and electrochemical devices. Many techniques allow for the simultaneous characterization of electrochemical materials and their performance (Luo and Weaver, 2001 Novak et al., 2000). Conductance cells provide a powerful approach to understanding of the structure-performance relationships at the molecular scale (Loridant et al., 1995). 

Carbon dioxide sensor — An electrochemical device for measuring the -+ partial pressure of carbon dioxide, originally developed for measurements with blood by Sever-inghaus and Bradley [i]. It consists of a glass electrode as used for pH measurements covered with a membrane selectively permeable for CO2, e.g., silicone. Between membrane and glass electrode an electrolyte solution containing NaCl and Na2C03 is entrapped. 

Hotta et al. [38] have developed a new electrochemical device for studying ET at the O/W interface, in which the O and W phases are separated by an electron conductor (e.g., Pt). This system is named as electron-conductor separating oil-water (ECSOW) system. As shown in Figure 8.3, the EC phase that separates the O and W phases can be feasibly realized by connecting two platinum disk electrodes with an electric wire. 

The new development is that electrochemical oxidation of ferrocyanide to ferricyanide can be coupled with asymmetric dihydroxylation to give a very efficient electrocatalytic process. The electrons necessary to the reoxidation of Fe(II) are provided by water that is reduced to OH and H2. Hydrogen gas, released at the cathode, is the only by-product of this process. This electrochemical device uses iron in catalytic amounts ( 0.15 equivalents per equivalent of olefin). 

Recently ionic liquid-based liquid crystalline materials have been developed as a new family of anisotropic (one or two dimensional) electrolytes [8, 26-29]. Ionic liquids are isotropic organic liquids composed entirely of ions [30-34]. They have advantages for applications as nonvolatile liquid electrolytes in a variety of electrochemical devices such as lithium ion batteries, capacitors, dye-sensitized solar cells, organic light-emitting diodes, and actuators. 

In addition to synthetic applications and the dissolution/deposition of materials, RTILs are also playing a key role in the development of new electrochemical devices including solar and fuel cells. 

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