Interface analysis electrolyte concentration

FIGURE 5.8 Theoretical analysis of an amphifunctionally electrified interface (a) effect of pH and externally applied potential on the interfacial double-layer potential and (b) potential necessary to apply across the interface to reach the isoelectric point as a function of pH. Electrolyte concentration, 0.01 M protolytic site density, 3 x 1018/m2 point of zero charge, pHPZC = 4.5 inner-layer capacitance, 0.05 F/m2 outer-layer capacitance, 0.30 F/m2. (Adapted from Duval, J., et al., Langmuir, 17, 7573, 2001.)... 

Lamperski, S., and C. W. Outhwaite. 1999. A non-primitive model for the electrode I electrolyte interface based on the Percus-Yevick theory. Analysis of the different molecular sizes, ion valences and electrolyte concentrations. Journal ofElectroanalytical Chemistry 460, no. 1-2 135-143. 

The impedance plots for the water/nitrobenzene interface are illustrated in Fig. 5. At frequencies approaching 5 kHz, the correction was made for the phase shift of the measured signal caused by the potentiostat itself. Sometimes a semicircular arc appears on the impedance plot frequencies and low electrolyte concentrations [23, 35], but suchn behaviour is probably due to the unsuitable cell construction or the potentiostat failure. The results of the analysis of the impedance plots shown in Fig. 5 are summarized in Table 1. With the increasing frequency co, the parameter X increases and its evaluation from the equation ... 

The molar concentration of the anion in the membrane at the interface C m can now be obtained from (4.3.21) since Capi is known. A similar analysis may be carried out for the " side of the membrane. Note that if the AN electrolyte concentration in the solution at the membrane-solution interface is C(k then, for CaSO, Caw = Cfsm-... 

In the application to strong electrolytes serious doubt exists whether the application of the complete cq. (40) is permissible because it implies certain internal inconsistencies which have been analys ed most extensively by Kirkwood But Casimir extending Kirkwood s analysis has shown that these inconsistencies do not arise (remain very small) when the complete eq. (40) is applied to the double layer on a large plane interface or on a large particle if the electrolytic concentrations in the whole system remain so small that in the bulk of the solution the limiting laws of Debye and Huckel form a reasonable approximation. 

The concentration of the transferred ion in organic solution inside the pore can become much higher than its concentration in the bulk aqueous phase [15]. (This is likely to happen if r <5c d.) In this case, the transferred ion may react with an oppositely charged ion from the supporting electrolyte to form a precipitate that can plug the microhole. This may be one of the reasons why steady-state measurements at the microhole-supported ITIES are typically not very accurate and reproducible [16]. Another problem with microhole voltammetry is that the exact location of the interface within the hole is unknown. The uncertainty of and 4, values affects the reliability of the evaluation of the formal transfer potential from Eq. (5). The latter value is essential for the quantitative analysis of IT kinetics [17]. Because of the above problems no quantitative kinetic measurements employing microhole ITIES have been reported to date and the theory for kinetically controlled CT reactions has yet to be developed. 

At present it is impossible to formulate an exact theory of the structure of the electrical double layer, even in the simple case where no specific adsorption occurs. This is partly because of the lack of experimental data (e.g. on the permittivity in electric fields of up to 109 V m"1) and partly because even the largest computers are incapable of carrying out such a task. The analysis of a system where an electrically charged metal in which the positions of the ions in the lattice are known (the situation is more complicated with liquid metals) is in contact with an electrolyte solution should include the effect of the electrical field on the permittivity of the solvent, its structure and electrolyte ion concentrations in the vicinity of the interface, and, at the same time, the effect of varying ion concentrations on the structure and the permittivity of the solvent. Because of the unsolved difficulties in the solution of this problem, simplifying models must be employed the electrical double layer is divided into three regions that interact only electrostatically, i.e. the electrode itself, the compact layer and the diffuse layer. 

Analysis of experimental data shows that the dependence of the geometrical parameters of oxides on the temperature and concentration of electrolyte is different for galvanostatic and potentio-static conditions (Fig. 35).221 It appears that potentiostatic anodization is limited mainly by processes in the bulk of the oxide and thus is not influenced by temperature (Fig. 35b), whereas the galvanostatic anodization regime involves oxide dissolution processes at the O/S interface depending both on Tel and Cel. 

Figure 3.63. Double layer on rutile example of a site-binding Interpretation. Electrolyte. KNO3. concentrations given. Drawn curves = model analysis. The open symbols are f-potentlals. (Redrawn from J.A. Davis. R.O. James and J.O. Leckie. J. Colloid Interface Set. 63 (1978) 480.)...

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