Calculation of the characteristics of Cl − and Br − ions adsorption on bismuth single-crystal planes from solutions in 2-propanol

Abstract

The values of the surface excess and the Gibbs energy of adsorption of halide ions on the (111) and (001) Bi single-crystal planes in solutions in 2-propanol have been calculated from the previously obtained experimental data using electrode potential as the independent electrical variable. It was found that under comparable conditions the results obtained at constant electrode potential and at constant electrode charge are coincident. The electrosorption valency and the dipole moment of the dipole formed by an adsorbed halide ion and its charge image in the Bi plane have been calculated. It was found that on the Bi(111) plane, where the chemical bonds are all saturated, the electrosorption valency does not depend on the electrode charge. In contrast, on the more active Bi(001) plane there is a noticeable dependence of the electrosorption valency on the electrode charge. The dipole value formed by an adsorbed halide ion and its charge image in Bi significantly diminishes when changing from negative to positive electrode charge density and at the higher positive charges the covalent bonding between the Bi(001) surface atoms and Br − anions is probable. The more complicated dependence of the dipole value on electrode charge at the Bi(111) planes was attributed to the change in solvent structure on the electrode surface. It was concluded that the dipole formed is significantly screened by the solvent molecules and the metal electron gas.