Application of Scale of Absolute Surface Potentials to the Reactions of Chemisorption and Electrocatalysis on Metals. Part 2

Abstract

The concepts of the absolute surface potential (ASP) E_S of the (hkl) facet of a metal crystal with E_S = ΔG_s/zF directly related to the Gibbs surface energy ΔG_S and with an equilibrium between (auto) adsorption of its own atoms on this facet of N_ad and negative charged surface vacancies (NCSV). On this basis, the ASP scale is a scale of adsorption potentials with point defects—the NCSV and adatoms, which determine their surface statistics as a result of the action of surface and electrostatic forces on these quasiparticles. This dualism is aimed at overcoming differences in the understanding of the surface potential in Helmgholz theory and Gibbs theory. The adsorption scale of the singular metal face has a special point—the potential of the zero charge (PZC) of the electrode $E_{{\text{N}}}^{0}{\text{ = }}-\Delta G_{{\text{S}}}^{0}{{(hkl)} \mathord{\left/ {\vphantom {{(hkl)} {zF}}} \right. \kern-0em} {zF}}$ with a minimum of adsorption of atoms and NCSV. Point of absolute adsorption devides the scale of cathodic and anodic polarization (Fig. 4.1, Part 1) with predominant adsorption of NCSV or adatoms, reaching the maximum degree at the potential of the second special point $E_{{\text{S}}}^{0}$ in each area of the ideal electrode polarization. Part 2 discusses the transition from the ASP to hydrogen scale using the ratio between the standard and absolute values ​​of a hydrogen electrode adopted by the International Union of Physical and Applied Chemistry. Combining the ASP scale with the scale of the absolute potentials of electrode reactions made it possible to calculate the electrode potential of a chemisorption and electrocatalytic reaction of hydrogen evolution on various metals, as well as the potential for the formation of passivating oxide on metals (Ni, Cr), known as the “Flade potential.”