Review COMPARISON AND DISCUSSION OF SOME THEORIES OF THE EQUILIBRIUM ELECTRICAL DOUBLE LAYER IN LIQUID ELJXTROLYTES l

Much past work on equilibrium properties of the electrical double layer is discussed. Particular attention is given to attempts to explain the differential capacitance of the double layer, with and without specific adsorption. Many theories of the inner and outer parts of the double layer are discussed, including continuum discrete, and lattice gas models. It is concluded that although adequate theories of the diffuse part of the double layer exist, none available so far is entirely adequate for the inner layer because of the strong lateral interactions present in it. (I) INTRODUff ION This paper deals with the electrical double layer (EDL- see list of acronyms at end of the paper) in thermal equilibrium. It is thus primarily concerned with the structure of the double layer, interactions between its discrete ionic and molecular components, and with its quasi-static, measurable differential capacitance. By contrast, the succeeding paper involves the steady-state, small-signal ac response (without or with dc bias) of systems involving double layers near electrodes. Such response, and its analysis, has been termed Impedance Spectroscopy [1,2]. When measurements are not limited to equilibrium conditions, important kinetic effects may occur. Long ago, Frumkin [3] first pointed out the importance of the EDL in affecting heterogeneous electron transfer reactions. The presence of an EDL affects the reaction because the electric field conditions in the reaction region near the electrode are different from those in the bulk of the material. The present paper is concerned primarily with nearly zero frequency response, and the second one with response covering a frequency range from low, an