Comparison of Two Recent Approaches Towards a Unified Theory of the Electrical Double Layer

摘要

In a paper, 'The Role of Ion-Ion Interactions in the Electrical Double Layer: Symmetrical Electrolytes Containing Equal Size Ions', recently published in this journal, Cooper and Harrison (CH) have proposed a model of the electrolyte double layer which attempts to unify inner and diffuse layer treatments. As CH state, a series of papers which also involve a unified approach to the same equilibrium double layer problem were available at the time their work was carried out. Since then, two more in this series have appeared. A theory of the electrical double layer recently proposed by Cooper and Harrison is compared to earlier, mainly lattice gas results. Detailed comparison of the Cooper-Harrison and lattice gas approaches reveals striking similarities as well as important differences. In both cases the charge density in the inner layer is derived from an effective potential. This potential is determined self-consistently as a function of the applied potential and the charge density itself. Close examination shows that the self-consistency equations are nearly identical. The main differences between the two approaches are the somewhat doubtful expression employed by Cooper and Harrison for the 'cut-off' radius for ion-ion interactions, and the much greater generality of the earlier theory.