Adsorption of bromide ions on bismuth single crystal planes from solutionsin ethanol

The adsorption of Br- ions on the (111), (001) and (01 (1) over bar) planes of the bismuth single crystal from solutions in ethanol has been investiga ted by differential capacity and electrode charge measurement methods. The ionic charge due to the specific adsorption has been obtained using the mix ed-electrolyte method for both electrode charge and electrode potential as the independent electrical variables. The Gibbs energy of adsorption of hal ide ions has been calculated using the simple virial adsorption isotherm. I t was found that under comparable conditions the results obtained at consta nt 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) < (01 (1) over bar) and solvents methanol < ethanol < 2-propanol. The electrosorption valency and the dipole moment of the dipol e formed by an adsorbed halide ion and its image charge in the Bi plane hav e been calculated. It was found that on the Bi(lll) plane, where the chemic al bonds are all saturated, the electrosorption valency has a constant valu e, while on the more active planes it depends on electrode charge. It was c oncluded that the surface dipole formed is screened significantly by the so lvent molecules and the metal electron gas. The surface dipole value dimini shes 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(lll) plane was attributed to the c hange in solvent structure on the electrode surface. (C) 2001 Elsevier Scie nce B.V, All rights reserved.