Redox process, electrochemical

Bipyridinium-type units (also known as viologens) are well-known electron acceptors64 extensively used in chemical and electrochemical redox processes,65 since they can undergo two reversible one-electron reduction processes. Because of these peculiar properties such units can be profitably used to functionalize the periphery of dendrimers, but examples of dendrimers containing a bipyridinium-type unit as a core are also reported.66... 

To ensure a sufficient electronic and thermal conductivity of the positive electrode during the charge and discharge process, conductive additives are required in the positive, transition metal oxide-based electrode.3133 Compared to metal powders as potential conductivity enhancer, carbon materials combine high electronic and thermal conductivity with low weight, low costs, relatively high chemical inertness, and nontoxicity. Conductive carbons optimize the electrical resistivity of the positive electrode mass but are not involved in the electrochemical redox process which delivers the... 

Review of literature concerning the photochemistry of inorganic compounds shows us that a substantial progress was achieved during the past two decades in understanding the photophysical and photochemical properties of nanometer semiconductor particles [1-4] and structurally organized semiconductor materials, including the nanostructured semiconductor films, mesoporous molecular sieves [5 - 10] etc., and, also in the elaboration of physical and chemical techniques for their synthesis and examination of their photocatalytic activity in various chemical and electrochemical redox-processes. 

In other redox, homogeneous catalytic reactions, palladium ions catalyze propylene oxidation to acetone 306). The Rashig process 307) is based on benzene oxidation with air in the presence of cupric and ferric chlorides. Toluene and xylene oxidize in solution containing organic salts of Co, Mn, and Mo 308,309). It is interesting to note that in some cases, reoxidation of the active metal ion to its original valence is assumed slow, for example, Cu(I) to Cu(II) 310). It is conceivable that such steps could be assisted and accelerated electrochemically. Conventional processes, then, can provide a starting point for the study and development of new electrochemical redox processes. 

Anode, cathode, and electrolyte are the three main elements in reversible electrochemical actuators and the conducting polymer actuators can he classified as extensional actuators and hydrostatic actuators. In order to perform mechanical work, linear or biaxial dimensional changes are used for the extensional actuators as illustrated in Figure 8.81 [134]. On the other hand, during the electrochemical redox processes, the overall volume change of the anode, cathode, and electrolyte is considered to perform the mechanical work in the hydrostatic actuators. 

Carbon materials are added to derrease the electrical resistivity of the electrode mass but generally are not involved in the electrochemical redox process which delivers the energy of the electrochanical ceU. To optimize the specific charge of the electrode as well as the energy density of the electrochemical cell, the amount of carbon in the total electrode volume needs to be minimized. The carbon quantity typically applied is below 10 wt% of the total electrode mass. Thus, in relation to the electrochemically active electrode material, the conductive carbon component can be considered to be electrode additive. 

Lee, C., Juhyoum, K., and Bard, A. J., Polymer films of electrodes. XXIV. Ellipso-metric study of the electrochemical redox processes of a polypyrrole film on a Pt electrode, J. Electrochem. Soc., 136, 3720-3724 (1989). 

Mainly sulphonate species have been chosen as internal dopant ions, because of their low reactivity in electrochemical redox processes. In this way, ionic transport in the conductive polypyrrole can be modulated by a high density of anionic sites, thus requiring the cation to be the mobile species. On the other hand, self-doped polymers can be electrochemically prepared without adding a salt to allow conduction [149]. Some of those self-doped materials are soluble in common solvents. 

The most serious problem of all photoelectrochemical devices is the susceptibility of semiconductors in contact with electrolytes to photodecomposition. Such decomposition reactions are electrochemical redox processes in which the semiconductor is involved and they can occur already in the dark. The electronic charge carriers of the semiconductors are direct reaction partners in these processes. The next table gives a summary over a number of decomposition reactions in which either holes or electrons participate. Since these reactions are electrochemical processes their thermodynamics can be described in terms of redox potentials at which these processes would be in equilibrium. 

FIGURE 11.6. Schematic diagram of a solid state electrolyte battery providiiig power to an external eireuit. The electrochemical redox process is that for an intercalation material, LixTiSj- (From Julien, C. and Nazn, G.A., SoUd State Batteries Materials Design and Optimization, Kluwer, Boston, 1994. With permission.)... 

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