Solvent effects in electrochemistry

Solvent effects in electrochemistry are relevant to those solvents that facilitate conductivities and electrode reactions. Together with the relative permittivity, that is responsible for the number of charge carriers per unit volume of the solution, the solvent... 

Solvent effects in electrochemistry are relevant to those solvents that permit at least some ionic dissociation of electrolytes, hence conductivities and electrode reactions. Certain electrolytes, such as tetraalkylammonium salts with large hydrophobic anions, can be dissolved in non-polar solvents, but they are hardly dissociated to ions in the solution. In solvents with relative permittivities (see Table 3.5) s < 10 little ionic dissociation takes place and ions tend to pair to neutral species, whereas in solvents with 8 > 30 little ion pairing occurs, and electrolytes, at least those with univalent cations and anions, are dissociated to a large or full extent. The Bjerrum theory of ion association, that considers the solvent surrounding an ion as a continuum characterized by its relative permittivity, can be invoked for this purpose. It considers ions to be paired and not contributing to conductivity and to effects of charges on thermodynamic properties even when separated by one or several solvent molecules, provided that the mutual electrostatic interaction energy is < 2 kBT. For ions with a diameter of a nm, the parameter b is of prime importance ... 

Refs. [i] Reichardt C (2003) Solvents and solvent effects in organic chemistry, 3rd edn. Wiley-VCH, Weinheim [ii] Aurbach D, Gofer Y (1999) The electrochemical window of nonaqueous electrolyte solutions. In Aurbach D (ed) Nonaqueous electrochemistry. Marcel Dekker, New York, pp 137-212 [Hi] Komorsky-Lovric S (2002) Electrolytes. In Scholz F (ed) Electroanalytical methods. Springer, Berlin, pp 279-299 [iv] KolthoffIM, WillmanA (1934) ] Am Chem Soc 56 1007... 

Refs. [i] Reichardt C (2003) Solvents and solvent effects in organic chemistry, 3rd edn. Wiley-VCH, Weinheim [ii] Aurbach D (ed) (1999) Nonaqueous electrochemistry. Marcel Dekker, New York... 

Gupta, N. and H. Linschitz (1997). Hydrogen-bonding and protonation effects in electrochemistry of quinones in aprotic solvents. J. Am. Chem. Soc. 119, 6384—6391. 

The third effective approach is the preparation of ionic Pcs with large balanced ions [69-77], It is well known that ionic compounds are usually more soluble than neutral compounds in most organic solvents, especially in polar and mixing solvents. Ionic Pcs include cationic and anionic Pcs. The preparation of ionic Pcs is usually by means of electrochemistry. Sometimes they can be synthesized through oxidation reactions, ion exchange reactions or ion coordination reactions. 

Subsequent investigations were undertaken of cobalt corroles with modified structures [77] and with cobalt in higher oxidation states [78]. In addition, cobalt-containing corrole dimers were studied [79], cobalt biscorroles were investigated ]80, 81], the influence of various alkyl and aryl substituents on the electrochemical behavior of cobalt corroles was probed ]82], and the effects of solvents on the electrochemistry of these compounds was examined [83]. 

The importance of solvents and their effects play roles in electrochemistry as well. The properties of a family of novel quaternary ammonium salts based on the bis(triflu-oromethylsulfonyl)imide and triflate anions are reported in a paper by Sun (Sun et al., 1998). Binary phase diagrams for some of their mixtures and their electrochemical windows of stability were reported. The highest conductivity observed in the pure salt systems at 25°C was 7 x 10 S cm-1. An electrochemical window of stability of up to 5V was measured on graphite electrodes. The effect of salt structure and solvent on conductivity of the salts is also discussed. 

This book was written to provide readers with some knowledge of electrochemistry in non-aqueous solutions, from its fundamentals to the latest developments, including the current situation concerning hazardous solvents. The book is divided into two parts. Part I (Chapters 1 to 4) contains a discussion of solvent properties and then deals with solvent effects on chemical processes such as ion solvation, ion complexation, electrolyte dissociation, acid-base reactions and redox reactions. Such solvent effects are of fundamental importance in understanding chem-... 

Chemical reactions in solutions are often affected drastically by the solvents used. The main objective of this book is to correlate the properties of solvents and the solvent effects on various chemical processes relevant to electrochemistry. The most important solvent properties in considering solvent effects are the solvent permittivity and the solvent acidity and basicity. If the permittivity of one solvent is high (er>30) and that of the other is low (er<10), the difference in a chemical process... 

From Mann s review, it is clear that the anion and the electrode material have a pronounced effect on the oxidation potentials of the nonaqueous systems. The metals to which the highest potentials can be applied in nonaqueous systems are obviously the noble metals (Pt, Au). The limiting reaction when the anions are halides (Cl-, Br, I ) was found to be their oxidation to the elemental form. When the anion is C104 , its oxidation onset at potentials above 1.5 versus Ag/ Ag+ may promote further intensive solvent degradation, as was found with ACN. It is important to note that using BF4 instead of C104- in ACN (which is an important and useful nonaqueous solvent in electrochemistry) extended its anodic stability limit by 2 V. 

In the second chapter, Appleby presents a detailed discussion and review in modem terms of a central aspect of electrochemistry Electron Transfer Reactions With and Without Ion Transfer. Electron transfer is the most fundamental aspect of most processes at electrode interfaces and is also involved intimately with the homogeneous chemistry of redox reactions in solutions. The subject has experienced controversial discussions of the role of solvational interactions in the processes of electron transfer at electrodes and in solution, especially in relation to the role of Inner-sphere versus Outer-sphere activation effects in the act of electron transfer. The author distils out the essential features of electron transfer processes in a tour de force treatment of all aspects of this important field in terms of models of the solvent (continuum and molecular), and of the activation process in the kinetics of electron transfer reactions, especially with respect to the applicability of the Franck-Condon principle to the time-scales of electron transfer and solvational excitation. Sections specially devoted to hydration of the proton and its heterogeneous transfer, coupled with... 

Faulkner et al. performed surface-confined electrochemistry at high pressures to probe the structure of the transition state during the oxidation of a tethered ferrocene probe (analogous to System 4) [139]. In these studies, the ferrocene-containing SAMs on gold were subjected to pressures between 1 and 6000 atm. The pressure dependence of the anodic peak potential reveals a positive volume of activation for oxidation, which is consistent with a solvent reorganization in the transition state, which allows ion complexation. This study demonstrates the importance of structural and environmental effects on surface-confined electron-transfer processes. 

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