Layered lattice gas model for the metal-electrolyte interface

Abstract

Several models of the diffuse double layer in liquid electrolytes are discussed. These models all involve partitioning the space charge region into a number of planar layers parallel to the metal electrode, with ionic liquid lattice gas, as opposed to idea gas, response in each layer. Each layer may contain both ions and solvent molecules. Several difficulties implicit in the earlier work of Liu on such a model are pointed out. These problems seem to have caused the appearance of an initial charge-free region in Liu's results. A layer model involving Liu's original assumptions of point ionic charges and point dipoles is discussed in detail and is shown to be electrostatically inconsistent. It is replaced by a layer model in which ionic charge resides on each basic layer, with each such layer surrounded symmetrically by charge layers representing the effect of finite-extent permanent dipoles. This model leads, as it should, to Gouy-Chapman behavior in the continuum limit. Finally, a method of including ion hydration effects explicitly in such a model is proposed.