On the Seventieth Birthday of Yu.V. Pleskov

Russian Journal of Electrochemistry -     

Equations for Transition from Grahame–Parsons Model to Alekseev–Popov–Kolotyrkin Model

Equations are derived, which allow one to determine the electrode's surface coverage with adsorbate, charge, differential capacitance, and interfacial tension within the framework of a phenomenological model, for which the Grahame–Parsons and Alekseev–Popov–Kolotyrkin models are the limiting cases.     

On the Seventieth Birthday of J. Japaridze

Russian Journal of Electrochemistry -     

Effect of Potential on Coadsorption of Two Organic Substances in the Frumkin Model at a Maximum Possible Number of Solutions for the Relevant Set of Isotherms

Effect of the electrode potential on the coadsorption of two organic substances is studied using a set of two mixed Frumkin isotherms and a model of three parallel capacitors in conditions where in the absence of an electric field this system has seven solutions. It is shown that only four of these solutions may correspond to realizable adsorption states. Effect of the electrode potential on the number of possible solutions of the isotherm set, the number of realizable adsorption states, as well as on the composition and properties of a surface layer is considered.     

Simulating Unstable States during the Coumarin Adsorption on a Mercury Electrode

Dependences of differential capacitance C on potential E of a stationary electrode (hanging mercury drop) in aqueous 0.1 M NaF solutions containing 4.6 × 10^–4 to 3 × 10^–3 M C₉H₆O₂ are obtained using an automatic impedancemeter. At coumarin concentrations below 0.001 M and potential slowly scanned near –1.1 V (SCE) the capacitance is unstable, which results in differently-shaped C vs. E curves in this potential range. The obtained results are attributed to nonequilibrium phase transitions in the adsorption layer, during which the orientation of coumarin molecules at the electrode surface alters. These phenomena are explained semiquantitatively on the basis of a developed theory.     

Double Electric Layer on Liquid Sn-Ga Alloy in Acetonitrile Solutions of Electrolytes

The structure of the double electric layer (DEL) on a liquid dropping Sn-Ga electrode containing 8 at. % of Sn is studied in acetonitrile (AN) solutions of electrolytes. It is shown that the transition from aqueous to AN solutions of electrolytes makes it possible to expand the region of investigation of parameters of DEL on an Sn-Ga electrode from negative charges to a zero charge and to small positive charges. As follows from the obtained data, throughout the entire interval of charges studied, an excess, as compared with an Hg electrode, chemisorption interaction (Sn-Ga)-AN is absent. It is established that the distance of the closest approach of AN dipoles to an ionic core increases upon going from Hg to Sn-Ga to Ga. The Ga, Bi-Ga, and Sn-Ga electrodes, which possess close values of the “electrochemical work function,” are used as an example to show that the metal-solvent chemisorption interaction increases with decreasing distance of the closest approach of its dipoles to the ionic core of the metal. The effect of this factor becomes stronger as the donor number of the solvent increases.     

Refining adsorption parameters of n-butyl alcohol at the interface of mercury electrode with aqueous NaF and Na2SO4 solutions by correcting the adsorbate concentration

As an adjunct to the regression analysis of differential capacitance curves, which allows refining the adsorption parameters, a program, which takes into account possible errors in volume concentrations of organic substances, is developed. Using this procedure, the earlier data on the differential capacitance of a mercury electrode in aqueous solutions of normal butanol (1-BuOH) containing either 0.1 M NaF or 0.05 and 0.5 M Na₂SO₄ as the supporting electrolyte are analyzed. This allows obtaining the most accurate values of adsorption parameters for the systems mentioned above within the framework of the model of two parallel capacitors and the Frumkin isotherm. It is shown that, when a linear dependence of the intermolecular interaction parameter on the electrode potential is taken into account, the standard deviation of experimental capacitance values from those calculated using the mentioned model is 6.8–8.8%, which points to very high accuracy of this phenomenological model.     

Some Anomalies in Coadsorption of Two Organic Substances Due to Differences in Molecular Interaction of Species Undergoing Coadsorption

Effect of molecular interaction between species undergoing coadsorption on the potential dependences of coverages ₁and ₂, surface tension, and equilibrium and nonequilibrium differential capacitances is analyzed on the basis of a set of isotherms for coadsorption of components 1 and 2 within a common monolayer when the EDL inner part obeys a model of three parallel capacitors. It is shown that, in a certain potential interval, at a certain ratio between adsorption parameters, the set of isotherms may have solutions that correspond to a minimum in a free energy surface, which is a function of ₁and ₂.     

Adsorption parameters of cyclobutane carboxylic acid at the interface of a mercury electrode with aqueous solutions of 0.4 M Na2SO4 + 0.1 M H2SO4

Based on the results of the regression analysis of differential capacitance curves of a mercury electrode in solutions of cyclobutane carboxylic acid (CBCA) at 25, 50, and 75°C, the adsorption parameters that enter into both the Frumkin isotherm and the model of two parallel capacitors are estimated. The free energies of adsorption found from the analysis of the temperature dependence of these parameters are incorrect due to the partial blowing out of CBCA during the deaeration of the solutions. The corresponding adsorption parameters are corrected under the assumption that the hydrophobic effect associated with the increase in the liquid-water entropy at the removal from it of CBCA molecules is the same as for n-valeric acid. The physical meaning of the squeezing-out effect is revised.     

Self-Consistent Calculation of Activity Coefficients and the Diffusion Layer Capacitance in Asymmetric Electrolytes

It is shown that substituting activities of individual ions for their concentrations in the equation for the ionic strength of solution substantially extends application of the first approximation of the Debye–Hückel theory for electrolytes of different valence. The obtained relationship predicts a changeover from the square root law in the charge region where the average distance between ions lis smaller than the ionic-atmosphere thickness 1/, to the cube root law, at l> 1/. The increasing deviation from experimental data upon going from LaCl₃solutions to La₂(SO₄)₃is attributed to the formation of ionic pairs LaSO₄ ⁺.