Adsorption of anions on bismuth single crystal plane electrodes from various solvents

The adsorption behaviour of Cl−, Br− and I− anions on Bi single crystal plane electrodes from aqueous, methanol, ethanol, 2-propanol and acetonitrile solutions has been studied by impedance spectroscopy and chronocoulometry methods. The values of the surface excess and Gibbs energy of adsorption of halide ions on the Bi(111), Bi(001) and Bi(011̄) single crystal planes have been calculated, using the electrode potential E and the surface charge density σ as the independent electrical variables. Analysis of data shows that, under comparable conditions, the results obtained at constants E and σ are coincident. The formal charge transfer coefficient (so-called electrosorption valency) and the dipole moment of the dipole, formed by a halide ion adsorbed and its image charge in the Bi plane, have been calculated. For the Bi(111) plane, where the chemical bonds are all saturated, the formal charge transfer coefficient and the dipole moment of adsorbed anion are practically independent of electrode potential. For more active Bi planes, there is noticeable dependence of both characteristics on the electrode charge, and at higher positive charges, the covalent bonding between Bi(011̄) surface atoms and I− is probable. Comparison of these data with those for vacuum ∣ metal interfaces shows that the dipole formed is significantly screened by the solvent molecules as well as by the metal electron gas, but the influence of the dielectric and other characteristics of solvent on the values of the effective dipole moment is comparatively small.