Adsorption of alkanes on a bismuth electrode from an alcoholic medium

The adsorption of higher alkanes (from C₁₀H₂₂ to C₂₁H₄₄) on a polarized bismuth electrode was studied from methanolic, ethanolic and n-butanolic solutions of LiClO₄ by differential capacity measurements. Alkane molecules, which do not contain either polar groups or double bonds, are compounds of low chemical activity. The adsorption of this group of compounds is purely physical. Nevertheless, a considerable difference in their adsorption activity on the various areas of the electrode surface caused by the two types of bond (metallic and covalent) between the atoms in the bismuth crystal lattice was discovered. Such a large difference indicates the different wettabilities of the separate single-crystal faces by alkanes. A weak dependence of the interaction parameter in the Frumkin isotherm on the length of the alkane molecule as well as on the length of the hydrocarbon chain of the solvent molecule was established. Various adsorption effects at high bulk concentrations of adsorbate (desolvation of the cations of the supporting electrolyte, thickening of the adsorption layer, maximum in the isotherm) were analysed.