Results of a Monte Carlo simulation of the electrode vertical bar electrolyte interface with and without solvent molecules are reported. The solvent molecules are modelled by neutral hard spheres immersed in a homogeneous dielectric medium. Calculations have been performed for 1: 1 and 1:2 electrolytes at c = 1M, with packing fraction eta = 0.3 when the solvent molecules were present, and at a wide range of electrode charge. Insertion of the solvent molecules induces a layering of ion and solvent molecules in the vicinity of the electrode surface. The presence of the solvent molecules reduces the thickness of the electric double layer, lowers the value of the mean electrostatic potential and raises capacitance. The differential capacitance results are compared with the MPB theory predictions. (c) 2006 Elsevier Ltd. All rights reserved.