Nonlocal dielectric response of the electrode/solvent interface in the double layer problem

Abstract

A theory of the double layer in the electrolyte solution near the electrode surface is formulated in terms of the most general description of the electrode/solvent interface, the ionic plasma being treated in the Poisson–Boltzmann approximation. As a result, the differential capacitance of the electrochemical contact is calculated. In the case of low ionic concentrations [Formula: see text] it takes the form: C−1 = CGC−1 + C*−1, where the CGC is the Gouy–Chapman nonlinear differential capacitance and C* is a "constant" capacitance, not depending on the concentration, but possessing a possible dependence on the charge of the electrode. The "compact layer" capacitance C* is expressed through a unified nonlocal dielectric function of the electrode–solvent system. This may be considered as a formal approval of Grahame's parametrization of experimental data. But the physical meaning of the compact layer capacity is reconsidered subject to the relation obtained with the nonlocal dielectric function. The latter reflects the electronic structure of the metal and the structure of the solvent in contact. Thereby, the possible reasons for the dependence of the "compact layer" capacity on the nature of the electrode, solvent, and the interaction between them are revealed. A generalization of the results on the case of a more general description of ionic plasma is discussed.