Adsorption of bromide ions on bismuth single crystal planes from solutions in ethanol

Abstract

The adsorption of Br - ions on the (111), (001) and (011) planes of the bismuth single crystal from solutions in ethanol has been investigated by differential capacity and electrode charge measurement methods. The ionic charge due to the specific adsorption has been obtained using the mixed-electrolyte method for both electrode charge and electrode potential as the independent electrical variables. The Gibbs energy of adsorption of halide ions has been calculated using the simple virial adsorption isotherm. It was found that under comparable conditions the results obtained at constant electrode potential and at constant electrode charge are coincident and the adsorption of Br anions increases in the sequence of Bi single crystal planes (111) < (001) < (011) and solvents methanol < ethanol < 2-propanol. The electrosorption valency and the dipole moment of the dipole formed by an adsorbed halide ion and its image charge 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 has a constant value, while on the more active planes it depends on electrode charge. It was concluded that the surface dipole formed is screened significantly by the solvent molecules and the metal electron gas. The surface dipole value diminishes when changing from negative to positive electrode charge and from the (111) plane to more active planes. The complicated dependence of the dipole value on the electrode charge at the Bi(111) plane was attributed to the change in solvent structure on the electrode surface.