Excess nonspecific Coulomb ion adsorption at the metal electrode/electrolyte solution interface: role of the surface...

Excess ion adsorption gamma induced by the polarization image forces in the system of a metal electrode/symmetric electrolyte solution separated by an insulating interlayer has been calculated. The adopted theoretical scheme involves the Coulomb Green's function in a three-layer system with sharp interfaces and specular reflection at them. The influence of the spatial dispersion of the dielectric permittivities epsilon(i)(k) in all the three media on the image force energy W(im) and the adsorption gamma has been analyzed, where k is the wave vector. A comparison with the classical model, where epsilon(i)=const, has been carried out. It has been shown that both the Debye-Hückel ion screening and the spatial dispersion of the solvent contribution epsilon(solv)(k) to the overall dielectric function epsilon(el)(k) of the electrolyte solution lead to the qualitative difference with the results for the classical model. In particular, in a wide range of ion concentrations n0 a thin interlayer L > or = 5-10 angstroms effectively screens out the attractive influence of the metallic electrode, so that the net Coulomb adsorption may become repulsive. The approach and the results obtained qualitatively describe two physically different situations. Specifically, the introduced interlayer corresponds either to the dense near-electrode (inner) electrolyte layer or to the intentionally deposited control coating of arbitrary thickness.