Impedance characteristics of iodide ions adsorption on Bi single crystal planes in ethanol

The impedance spectra for Bi(1 1 1), Bi(0 0 1) and Bi(0 1 1̄) single crystal planes in 0.1 M LiI solution in ethanol have been measured. It was found that reproducible experimental data for Bi electrodes in ethanol solutions could be obtained in the range of ac frequencies between 0.1 and 10,000 Hz and electrode potentials −1.6<E<−0.2 V (vs. aqueous SCE). Outside this potential region the occurrence of faradaic processes was detected. By fitting the experimental data to various equivalent circuits it was found that the Frumkin–Melik-Gaikazyan model yields a good fit at E<−0.6 V, but at E⩾−0.6 V, more complex equivalent circuits should be introduced. Using these models the dependences of “true” and adsorption capacitances as well as diffusion resistance on electrode potential have been obtained. It was proposed that, at E>−0.6 V for all Bi single crystal planes studied, the formation of a surface compound is probable.