The capacitive behaviour of interfaces between aqueous solutions of non-specifically adsorbing electrolytes and Hg, Bi(111) and Ga electrodes has been studied on the basis of a quantum chemical approach and using a simple lattice model in the mean field approximation. Dependencies of the compact layer differential capacitance (C-H) on the electrode surface charge density (sigma) have been constructed and compared with the experimental data. A significant difference in the C-H(sigma) dependence observed in the experiment with different metal electrodes has been explained in terms of the interplay between contributions from metal electrons and adsorbed solvent molecules. New data elucidating the metal-water adsorption bond have been reported as well. (C) 2016 Elsevier Ltd. All rights reserved.