Thermodynamics electrical double-layer structure

The subsequent three chapters are devoted to the electric double-layer structure at the interface between immiscible electrolytes examined by the electrocapillary curves method (Prof. Senda and coauthors) and by measurement of the electric double-layer capacity (Dr. Samec and Dr. Mare ek) as well as to the investigation of the Galvani and Volta potentials in the above-mentioned systems (Prof. Koczorowski). These chapters will be of interest to many electrochemists since the results obtained here are comparable with the thoroughly studied metal/electrolyte solution interface. An insignificant potential shift in the compact layer at the interface between immiscible electrolytes in the absence of specific ion adsorption - this is the main conclusion arrived at by the authors of Chaps. 4 and 5. Chapter 6 deals with the scale of potentials in a system of immiscible electrolytes and the thermodynamic relation between the distribution coefficients and the Volta potentials. 

The thermodynamic theory of electrocapillarity considered above is simultaneously the thermodynamic theory of the electrical double layer and yields, in its framework, quantitative data on the double layer. However, further clarification of the properties of the double layer must be based on a consideration of its structure. 

In order to determine a system thermodynamically, one has to specify some independent parameters (e.g. N, T, P or V) besides the composition of the system. The most common choice in MC simulation is to specify N, V and T resulting in the canonical ensemble, where the Helmholtz free energy A is the natural thermodynamical potential. However, MC calculations can be performed in any ensemble, where the suitable choice depends on the application. It is straightforward to apply the Metropolis MC algorithm to a simple electric double layer in the iVFT ensemble. It is however, not so efficient for polymers composed of more than a few tens of monomers. For long polymers other algorithms should be considered and the Pivot algorithm [21] offers an efficient alternative. MC simulations provide thermodynamic and structural information, but time-dependent properties are not accessible. If kinetic or time-dependent properties are of interest one has to use molecular dynamic or brownian dynamic simulations. 

The first section of this book covers liquids and. solutions at equilibrium. I he subjects discussed Include the thcrmodvnamics of solutions, the structure of liquids, electrolyte solutions, polar solvents, and the spectroscopy of solvation. The next section deals with non-equilibrium properties of solutions and the kinetics of reactions in solutions. In the final section emphasis is placed on fast reactions in solution and femtochemistry. The final three chapters involve important aspects of solutions at interfaces. Fhese include liquids and solutions at interfaces, electrochemical equilibria, and the electrical double layer. Author W. Ronald Fawcett offers sample problems at the end of every chapter. The book contains introductions to thermodynamics, statistical thermodynamics, and chemical kinetics, and the material is arranged in such a way that It may be presented at different levels. Liquids, Solutions, and Interfaces is suitable for senior undergr.iduates and graduate students and will be of interest to analytical chemists, physical chemists, biochemists, and chemical environmental engineers. 

Structural features of disperse systems, in particular the existence of the electrical double layer (EDL), are responsible for a number of peculiar phenomena related to heat and mass transfer and electric current propagation in such systems. The description of electromagnetic radiation propagation is also included in this chapter. These features are utilized in numerous practical applications and underlie methods used to study disperse systems. These methods include particle size distribution analysis, studies of the surface structure and of near-surface layers, the structure of the EDL, etc. In the most general way the most transfer phenomena can be described by the laws of irreversible thermodynamics, which allow one to carry out a systematic investigation of different fluxes that originate as a result of the action of various generalized forces. 

Thus the theory of change in the water structure on the mineral particle surface is close to the theory of the electric double layer with the difference that in the first case the water acts as an electrolyte and mechanisms intensifying the process of the electric double layer formation are not the electric fields but the thermodynamic ones (temperature and pressure). 

The electrical double layer arising at the ITIES has been studied by measuring the surface tension [4, 7-16, 25] or the impedance [17-26] mainly of water/nitrobenzene [4, 7-15, 17, 19-24] and water/l,2-dichlorethane [12, 16, 18, 25, 26] systems. This contribution reviews the principles and the results of the impedance measurements, in particular those based on the AC impedance or galvanostatic pulse techniques, which have been used most frequently for the study of the double layer at the ITIES. The quantity, which can be inferred from the impedance measurements, and which is related to the double-layer structure, is the interfacial capacitance. We shall discuss first the thermodynamic background for the capacitance of the electrical double layer at the ITIES. 

Experimentally, the electrical double-layer affect is manifest in the phenomenon named electrocapillarity. The phenomenon has been studied for many years, and there exist thermodynamic relationships that relate interfacial surface tension between electrode and electrolyte solution to the structure of the double layer. Typically the metal used for these measurements is mercury since it is the only conveniently available metal that is liquid at room temperature (although some work has been carried out with gallium. Wood s metal, and lead at elevated temperature). 

When ionic liquid systems are intended to be applied for electrodepwsition their behaviour has to be assessed as comp>ared with the case of aqueous electrolytes. The main factors which affect the overall electrochemical process include viscosity, conductivity, the potential window, the ionic medium chemistry as well as the structure of the electrical double layer and redox potentials. All these prarameters will influence the diffusion rate of metallic ions at the electrode surface as well as the thermodynamics and kinetics of the reduction process. Consequently, the nudeation/growth mechanisms and the deposit morphology will be affected, too. More detailed discussions on this topic may be formd in ( Abbott et al., 2004 Abbott et al., 2004 Abbott McKenzie, 2006 Abbott et al., 2007 Endres et al., 2008 and included references). 

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