An ion-dipole mixture against a charged hard wall with specific adsorption

Abstract

The electric double layer is modelled by a hard-sphere ion–dipole mixture in the neighbourhood of a uniformly charged plane hard wall. Specific adsorption of the ions and dipoles are treated using Baxter's sticky potential. The theory is investigated for 1:1 electrolytes in the mean-field approximation. The inclusion of different ion sizes and dipole adsorption leads to a variety of differential capacitance curves. In some situations a maximum can occur in the capacitance which is reminiscent of a ‘hump’ observed in experimental work.