Journal of Electroanalytical Chemistry 445 (1998) 165 – 170 An impedance and chronocoulometric study of the adsorption of chloride and bromide ions on bismuth single crystal planes from solutions in methanol M. Va ¨a ¨rtno ˆ u *, E. Lust Institute of Physical Chemistry, Uniersity of Tartu, Jakobi 2, EE2400 Tartu, Estonia Received 12 August 1997; received in revised form 24 November 1997 Abstract The adsorption of Cl - and Br - ions on the (111), (001) and (011  ) planes of a bismuth single crystal electrode from solutions in methanol has been investigated by means of differential capacity and coulometric measurements. The ionic charge due to the specific adsorption has been obtained using the mixed-electrolyte method. The results have been analysed and some characteristics calculated by the simple virial adsorption isotherm and classical inner layer model. It has been found that the difference in the adsorption characteristics for various planes of the Bi single crystal is rather small in methanol and it depends on solvent nature in a quite complicated manner. The analogous difference in inner layer capacity in methanol has been found to be close to that difference in ethanol and water, but much lower than in 2-propanol. © 1998 Elsevier Science S.A. All rights reserved. Keywords: Adsorption; Ions; Methanol; Bismuth; Alcohols; Single crystal 1. Introduction Investigation of the adsorption of inorganic anions on various planes of bismuth single crystals in different solvents [1 – 3] indicated that the adsorption properties of these planes are significantly dependent on the na- ture of the solvent. The differences in adsorption and double layer parameters between various planes were most notable when comparing the results in water and ethanol. For example, the dispersion of potentials of zero charge (E  =0 ) is very low in ethanol (less than 30 mV) but quite significant in water (up to 90 mV) [4]. On the other hand, the characteristics of the halide ion adsorption on various planes are closer in water than in ethanol and 2-propanol [3]. Considering the remarkably different influence of the crystallographic structure of the electrode surface on the electrochemical properties of the metalsolution in- terface in water and ethanol, it is of interest to establish the extent of that influence in methanol. The E  =0 values for different planes of Bi single crystals in methanol have been already estimated [4] and the dis- persion of these values was found to be about 60–70 mV, i.e. between those of water and ethanol and close to the 2-propanol value. The aim of the present study is to estimate the characteristics of Cl - and Br - ion adsorption from methanolic solutions on the (111), (001) and (011  ) planes of the Bi single crystal and to compare the results for various alcohols and water. The Bi(111) plane (basal plane) differs from others by the different binding orbitals of surface atoms; the (011  ) and (001) planes differ mainly by superficial densities of surface atoms [4]. 2. Experimental Two experimental methods were used for studying of the adsorption of Cl - and Br - ions on the * Corresponding author. Fax: +372 7 465160; e-mail: martv@mega.chem.ut.ee 0022-0728/98/$19.00 © 1998 Elsevier Science S.A. All rights reserved. PII S0022-0728(97)00606-2