ANALYSIS OF THE APPLICATION OF THE DOGHONADZE-KUZNETSOVALEVYCH THEORY IN THE STUDY OF THE ELEMENTARY ACT OF THE RED|OX PROCESS AT THE SOLID-ELECTROLYTE INTERPHASE BOUNDARY

Abstract

The purpose of this work was to generalize the Dogonadze-Kuznetsov-Levich theory for the calculation of oxidationreduction processes at the dielectric-electrolyte interface and, based on the calculations, to substantiate the possibility of the surface conductivity of the dielectric in salt melts. It is shown that the transition of the surface layer of the dielectric to the conductive state consists in the redistribution of the electron density between the adsorbent and the adsorbate, which leads to corresponding changes in the Fermi energy of the surface electrons of the electrode and the energies of the marginal molecular orbitals of the EAC. The dominant effect of this effect is the equalization of the Fermi energy levels of the cathode material and the energies of the HVMO EAC. It was established that in order for the redox process on a solid to take place actively, it is necessary for the Fermi level to be located inside the conduction band or the valence band, and the immersion of the Fermi level by a distance equal to or greater than 4kT into the band leads to the fact that the surface of a solid body exhibits an electrochemical function similar to that of a metal (metallizes), while the band gap can be large. It was found that the position of the Fermi level relative to the edges of the conduction band and valence band can be changed by an external electric field directed perpendicular to the surface of a solid body or by the polarizing action of a molecule or ion adsorbed on the surface of a solid body. An external electric field leads to a tilt of energy levels in a solid body, as a result of which a surface potential arises, that is, a bending of zones on the surface. The sign of the external electric field determines the direction of bending of energy zones. At the same time, if a solid body is used as a cathode, that is, a cathodic overvoltage is applied to the solid body, then the zones bend downward, which leads to the Fermi level approaching the lower edge of the conduction band and simultaneously moving away from the upper border of the valence band. Accordingly, with anodic overvoltage, the situation changes to the opposite. The external electric field does not change the width of the band gap and the position of the Fermi level. Cathodic overvoltage applied to the surface brings the Fermi level closer to the edge of the conduction band on the crystal surface, but does not change the band gap (about 5.5 eV). At high cathodic overvoltages, the Fermi level can approach the minimum of the conduction zone, which will lead to the degeneration of the electron gas, and the solid body (dielectric) will begin to exhibit an electrochemical function similar to that of a metal. The heterogeneity of the electric field leads to the fact that the energy levels on the surface of the solid body are bent differently, which leads to a change in the width of the band gap and the distance from the Fermi level to the border of the conduction band or valence band. At the same time, the nature of the surface polarization depends on both the adsorbed ion and the solid body itself. Thus, the same ion can polarize the surface of a solid in different ways.