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

The values of the surface excess and the Gibbs energy of adsorption of hali de ions on the (111) and (001) Bi single-crystal planes in solutions in 2-p ropanol have been calculated from the previously obtained experimental data using electrode potential as the independent electrical variable. It was f ound that under comparable conditions the results obtained at constant elec trode potential and at constant electrode charge are coincident. The electr osorption 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 w as found that on the Bi(111) plane, where the chemical bonds are all satura ted, the electrosorption valency does not depend on the electrode charge. I n contrast, on the more active Bi(001) plane there is a noticeable dependen ce 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 attribut ed to the change in solvent structure on the electrode surface. It was conc luded that the dipole formed is significantly screened by the solvent molec ules and the metal electron gas. (C) 2000 Elsevier Science Ltd. All rights reserved.