Impedance study of chloride ions adsorption on Bi(1 1 1) and Bi(011¯) single crystal planes in ethanol

The impedance spectra for Bi(111) and Bi(011¯) single crystal planes in 0.1, 0.02 and 0.005 M LiCl solutions in ethanol have been measured in the range of ac frequencies between 0.1 and 10 000 Hz and electrode potentials −1.4 < E < −0.2 V (vs. aqueous saturated calomel electrode). By fitting of the experimental data to various equivalent circuits, it was found that the Frumkin-Melik-Gaikazyan model yields to the good fit in almost the whole potential range studied. Using this model, the dependencies of “true” and adsorption capacitance on electrode potential have been calculated. The ionic charge due to the specific adsorption of Cl− ions has been obtained using the mixed-electrolyte method in 0.1 M solutions for both electrode charge and electrode potential as the independent electrical variables. The Gibbs energy of adsorption of Cl− ions has been calculated using the simple virial adsorption isotherm. It was found that the adsorption of Cl− anion increases in the sequence of Bi single crystal planes (111)<(001)⩽(011¯) and solvents methanol < ethanol < 2-propanol. It was found that the electrosorption valency has a constant value in the potential range studied. It was concluded that the formed effective surface dipole is significantly screened by the solvent molecules and the metal electron gas.