Electrochemical potentials solvent effects

The current chapter focuses on the electrochemistry of the ionic forms of copper in solution, starting with the potentials of various copper species. This includes the effect of coordination geometry, donor atoms, and solvent upon the electrochemical potentials of copper redox couples, specifically Cu(II/I). This is followed by a discussion of the various types of coupled chemical reactions that may contribute to the observed Cu(II/I) electrochemical behavior and the characteristics that may be used to distinguish the presence of each of these mechanisms. The chapter concludes with brief discussions of the electrochemical properties of copper proteins, unidentate and binuclear complexes. 

This chapter deals with the fundamental aspects of redox reactions in non-aque-ous solutions. In Section 4.1, we discuss solvent effects on the potentials of various types of redox couples and on reaction mechanisms. Solvent effects on redox potentials are important in connection with the electrochemical studies of such basic problems as ion solvation and electronic properties of chemical species. We then consider solvent effects on reaction kinetics, paying attention to the role of dynamical solvent properties in electron transfer processes. In Section 4.2, we deal with the potential windows in various solvents, in order to show the advantages of non-aqueous solvents as media for redox reactions. In Section 4.3, we describe some examples of practical redox titrations in non-aqueous solvents. Because many of the redox reactions are realized as electrode reactions, the subjects covered in this chapter will also appear in Part II in connection with electrochemical measurements. 

To describe the mass transport in an electrolyte solution or in an ion-exchange membrane, three independent fluxes must be considered, that is, the fluxes of the cations the flux of anions, and the flux of the solvent [16]. The transport of ions is the result of an electrochemical potential gradient and the transport of the solvent through the membrane is a result of osmotic and electro-osmotic effects. 

Another problem, often important when dealing with Marcus correlations may arise when the potentials are known in one solvent while the kinetic experiments are made in another one. Calculation of dG requires inclusion of the effect of solvent change on the electrochemical potentials. The usual procedure considers the difference in the solvation energies of the ions according to the Born equation. For instance, when using acetonitrile measurements to evaluate values in benzene, Eq. (8) may be used [97, 98],... 

As a final note concerning solvent effects, amphiphilic alcohols added to hydro-phobic electroactive n-alkanethiol SAMs in aqueous solution appear to aggregate on the monolayer surfaces, decreasing the capacitive envelope and enhancing the barrier properties [109, 110]. However, the formal potentials of the redox couples are shifted positively, and the electrochemical reversibility is decreased. This effect had previously been used by Becka and Miller to determine the pinhole current in the presence of a freely diffusing redox probe (see above) [96]. 

Cobalt(II,III) sepulchrates have been used in the chemical education [415] and considerable number of the chemical and physicochemical studies as efficient quencher of the phosphorescence [416] and electronic excited states [417, 418], as a reductant in kinetic studies of redox reactions [419, 420], as a model for study of magnetodynamic [421], solvent [422] and pressure [423] effects on the outer-sphere electron-transfer reactions. Transfer chemical potentials (from solubility measurements) [424], electrochemical reduction potentials [425] and ligand-field parameters [426] for cobalt sepulchrates have been calculated. Solvent effect on Co chemical shift of cobalt(III) ion encapsulated in the sepulchrate cavity [427]... 

The solvent effect on electrochemical oxidative and reductive desorption of alkanethiolate monolayers and rates of desorption at different potentials was studied by Everett and... 

In addition to the solvent contributions, the electrochemical potential can be modeled. Application of an external electric field within a metal/vacuum interface model has been used to investigate the impact of potential alteration on the adsorption process [111, 112]. Although this approach can model the effects of the electrical double layer, it does not consider the adsorbate-solvent, solvent-solvent, and solvent-metal interactions at the electrode-electrolyte interface. In another approach, N0rskov and co-workers model the electrochemical environment by changing the number of electrons and protons in a water bilayer on a Pt(lll) surface [113-115]. Jinnouchi and Anderson used the modified Poisson-Boltzmann theory and DFT to simulate the solute-solvent interaction to integrate a continuum approach to solvation and double layer affects within a DFT system [116-120]. These methods differ in the approximations made to represent the electrochemical interface, as the time and length scales needed for a fiilly quantum mechanical approach are unreachable. 

In any chemical separation scheme, the original sample becomes divided into at least two firactions through the application of a driving force across a functional boundary in such a way that the resulting firactions have a chemical fingerprint that is distinctly different from that of the initial sample. Typical driving forces are concentration gradients, solvent flow, or electrochemical potential. Typical separation boundaries include immiscible liquid-liquid or liquid-solid interfaces. The effectiveness of the separation of contaminant A from desired material B can be expressed in terms of a decontamination factor D ... 

The reduction potential, Eq, or the closely related electrochemical potential equals the ionization potential of the reduced spede plus solvent effects [25]. On the other hand the ionization potential of a metal surface i.e. the work function, 0, equals the chemical potential plus the surface barrier [25]. Hence the empirical ratios, =65cm and =... 

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