Impedance Study of Adsorption of Chloride Ions in Ethanol on Bi(001) Single Crystal Plane

Abstract

The impedance spectra for Bi(001) single crystal plane in 0.1, 0.02 and 0.003 M LiCl solutions in ethanol have been measured. It was found that reproducible experimental data for Bi electrode in ethanol solutions could be obtained at ac frequencies between 0.1 and 10 000 Hz and electrode potentials from -1.6 to -0.2 V (vs saturated calomel electrode). Outside this potential region, faradaic processes were detected. By fitting the experimental data to various equivalent circuits it was found that the Frumkin-Melik-Gaikazyan model yields good fit in almost the whole potential range studied. Using this model the dependences of "true" and adsorption capacitance as well as diffusion resistance on electrode potential have been obtained. 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 electric variables. The Gibbs energy of adsorption of Cl- ions has been calculated using a simple virial adsorption isotherm. It was found that the adsorption of Cl- anion increases in the order methanol < ethanol < propan-2-ol. It was found that on the Bi(001) plane 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.