I. A. Bagotskaya

Potentials of zero charge, interaction of metals with water and adsorption of organic substances—I. Potentials of zero charge and hydrophilicity of metals

The most reliable values of the potentials1 of zero charge for metals not adsorbing hydrogen are obtained from the position of the minimum on the differential capacity-potential curves. These data are confirmed by the scrape method and by electron photoemission measurements. However, as it was first found from the comparison of the behaviour of gallium and mercury, at the same potentials referred to pz the adsorption behaviour of various electrodes with respect to the simplest aliphatic surfactants—aliphatic alcohols—differs. This was explained by preferential water chemisorption at electrodes of the gallium type. The determination of the position of the differential capacity curve of the amyl alcohol desorption peak relative to pzc gives a semi-quantitative estimate of the hydrophilicity of various metals, inreasing in the sequence Hg < Bi < Sn < Pb < Cd < In < Ga. The potential at which the differential capacity of the dense layer starts to increase with decreasing negative charge shifts to more negative values relative to pzc in a similar sequence. The obtained results are compared with Trasattis data. The case of antimony requires further investigation.

The influence of crystallographic inhomogeneity of a polycrystalline electrode surface on the behavior of the electric double-layer

Abstract The specific features of the electric double-layer structure at polycrystalline electrodes in the absence of specific ion adsorption have been examined for two different models: Model I and Model II. In the case of Model I each of the faces showing on the surface of a polycrystalline electrode retains its own Helmholtz and diffuse double layers. In the case of Model II the faces retain only their own Helmholtz layer, whereas the diffuse layer is common to the entire electrode surface. The difference of zero charge potentials of the faces is defined both by their dissimilar hydrophilic properties and by different work functions. The experimental data available at present on the electric double-layer structure at polycrystalline electrodes for which the potentials of zero charge of the faces differ significantly are described by Model I.

Metal-solvent interaction and ion adsorption: Influence of solvent and metal nature

Abstract The influence of the lyophilic properties of an electrode on the specific adsorption of ions is analyzed by comparing the electric double-layer structure at mercury, bismuth and eutectic (In + Ga) alloy in acetonitrile and dimethylsulfoxide in inactive electrolyte solutions and in solutions containing surface-active ions. A method is proposed for estimating the free energy of interaction of solvent molecules with the electrode surface from adsorption isotherm parameters. It is shown, as exemplified by dimethylsulfoxide, that the lyophilic series of metals established from differential capacity values in inactive electrolyte solutions correlates with the change in the values of the free energy of interaction of dimethylsulfoxide molecules with the electrode, estimated by the method proposed in this paper. The influence of the nature of the electrode and the salvation energy of ions in different solvents on the surface activity series of these ions is examined.

Potentials of zero charge, interaction of metals with water and adsorption of organic substances—II. Potentials of zero charge and the work function

Abstract The factors have been considered which can lead to a discrepancy between the difference of the potentials of zero charge and the difference of the work functions. It has been shown that some discrepancies are eliminated if instead of the potentials of zero charge, we compare the potentials corresponding to the same and sufficiently large negative electrode charge, thus ensuring the same interaction between the electrode surface and water dipoles. This method is however inapplicable to metal phases of variable composition if the pzc of their components differ significantly.

The role of metal and solvent in the structure of the electrode|surface-inactive electrolyte solution interface

Abstract The effect of the electronic properties of the metal on the structure of an electric double layer was investigated using Hg, Ga, In–Ga and Tl–Ga electrodes in water, ethanol, n-propanol, acetonitrile, ethylene carbonate and N-methylformamide as examples. In the absence of any chemisorption interaction between the metal and the solvent, the closest distance of solvent dipoles to the surface of Hg was shown to differ from that of the gallium subgroup metals. The difference in these distances depends on the metal nature but not on that of the solvent; it does not depend on the electrode charge either. With due allowance for differences in the distances of solvent dipoles to the surface of different metals, the concept of the lyophilic nature of metals relative to solvents may be altered radically.

Solvent effects in the electric double-layer structure for gallium and gallium-like metals

Abstract Effects of a specific interaction between the solvent and the metal in the electric double layer structure in a surface-inactive electrolyte solution are considered, based on experimental data for the gallium group of metals in various solvents: water, acetonitrile, dimethylsulphoxide, dimethylformamide and N-methylformamide. A donor-acceptor interaction between the metal and chemisorbed solvent molecules is shown to exist, the solvent being an electron donor with respect to the metal. The problem of orientation of chemisorbed solvent molecules at a uncharged metal surface is analysed.

Structure of Electrical Double Layer on Liquid Pb–Ga Alloy in Aqueous Electrolytes

A new electrode, which is a liquid Pb–Ga alloy (0.06 at. % Pb), is developed and studied. It is shown that the alloys double-layer characteristics dramatically differ from characteristics of a Ga electrode and are practically identical to characteristics of a Pb electrode. Hence, the Pb–Ga electrode in fact models electrochemical properties of a liquid Pb electrode. It is established that the “metallic” capacitance of the Pb–Ga electrode occupies an intermediate position between values of metallic capacitance of Ga and Hg electrodes, provided the metal–water chemisorption interaction is absent and the electrode charge is fixed. Hydrophilicity of the Pb–Ga electrode is substantially lower than hydrophilicity of a Ga electrode and coincides with hydrophilicity of an Hg electrode. It is shown that In–Ga, Cd–Ga, and Pb–Ga electrodes have close values of the electrochemical work function, and the chemisorption potential drop of the solvent in them increases in the series Pb–Ga < In–Ga < Cd–Ga with decreasing distance of closest approach of water molecules to the ionic core of the metal. The absorbability of anions at the Pb–Ga electrode increases in the series BF–4= SO2–4< Cl–< Br–< I–.

Electrical Double Layer at a Liquid Pb–Ga Electrode in Propylene Carbonate Solutions

Differential-capacitance curves and potentials of zero charge are obtained for a liquid Pb–Ga electrode in propylene carbonate (PC) solutions of surface-inactive electrolyte LiBF4and 0.1 M solutions of LiBr and LiI. In PC and water, double-layer parameters of Pb–Ga differ from those of Ga. The lyophilicity of Pb–Ga in respect to PC is lower than that of Ga and coincides with that of Hg.