Cyclic voltammetry (CV) and electrochemical impedance spectroscopy have been employed for the quantitative study of 1,6-hexanediol (HD) adsorption at the Bi(001) and Bi(111)vertical bar 0.05 M Na2SO4 aqueous solution interfaces. According to the experimental data the Bi(111) interface has more negative zero charge potential and the adsorption-desorption peaks appear at more negative potentials than in case of Bi(001) interface. However, the adsorption activity is practically similar for Bi(001) and Bi(111) planes. The surface area occupied by one adsorbed molecule S-max equal to 0.47 nm(2) at the maximum adsorption potential indicates that HD molecules have flat orientation on Bi(hkl) surfaces. For less concentrated solutions the capacitance decreases in the maximum adsorption area as HD concentration increases, but in case of HD concentrations above 0.5 M the capacitance starts to increase. Cyclic voltammetry results show the capacitive adsorption and desorption peaks at higher potential scan rates for solutions with addition of HD in the base electrolyte solution. (c) 2006 Elsevier Ltd. All rights reserved.