New theoretical description of electrified interfaces

Starting from a Landau-Ginzburg-like Hamiltonian we have analysed an extension of the Gouy-Chapman theory. It contains three phenomenological parameters describing the overall effect of interionic correlations. We show that the expression for the differential capacitance takes a simple and very suggestive form. We use a numerical method to calculate ionic profiles and diffuse layer capacitance. Depending on the parameters, a variety of behaviours for the charge dependence of capacitance can be generated. We discuss the consequences of our model for the interpretation of experimental data based on the Parsons-Zobel plot.