Influence of electrical images and electrolyte concentration on capacitance of the electrode - molten salt interface

Abstract

Results of Monte Carlo grand canonical ensemble simulations of electrical double layer (EDL), with and without electrical images on the electrode, are presented. Calculations were carried out for a wide range of electrode surface charge, σ from -0.7 to 0.7 Cm−2 and a wide range electrolyte concentrations, c = 1.00 – 8.67 M. The electrolyte concentration of 8.67 M corresponds to the density of molten salts. It is known from earlier studies that for low electrolyte concentrations and low electrode charges, the EDL capacitances obtained for electrical images included in the calculations are greater than those calculated excluding them. For high electrolyte concentrations, especially for those which correspond to the molten salt densities, the situation unexpectedly turns around, i.e. the EDL capacitances obtained for the case of excluded images are greater than those calculated including them. For the whole range of applied electrolyte concentrations and electrode charges greater than σ ≈ 0.4 Cm−2 and lower than σ ≈ -0.4 Cm−2 no visible influence of applying the electrical images is observed on the EDL capacitance values. The above observations are discussed, explained in terms of the relationship between EDL thickness and the capacitance value, and analysed in terms of the electrostatic interactions of ion charges with their images.