Electrified Interfaces and Their Electrical Potentials

An electric potential drop across the boundary between two dissimiliar phases as well as at their surfaces exposed to a neutral gas phase is the most characteristic feature of every interface and surface electrified due to ion separation and dipole orientation. This charge separation is usually described as an ionic double layer. 

The system of distinctions and terminology of the thermodynamic and electric potentials introduced by Lange is still very useful and recommended for describing all electrified phases and interphases. Therefore these potentials can be assigned to metal/solution (M/s), as well as the liquid/liquid boundaries created at the interfaces of two immiscible electrolyte solutions water (w) and an organic solvent (s). 

The Volta potential, A very often called the contact potential, is the difference between the outer potentials of the phases, which are in electrochemical equilibrium in regard to the charged species, i.e., ions or electrons. Each two-phase electrochemical system, including a w/s system, may be characterized by the commonly known relation  

The Volta potential, in contradiction to the Galvani potential, has the advantage of being measurable but also the disadvantage that it is not determined only by the chemical nature of the phases that create the interface, but also by the state at their surfaces, represented by the surface potentials, Eqs. (1) and (2). 

In principle, the distribution of ions and dipoles at the M/s interface is different from that at the free M and s surfaces. Therefore the Galvani potential may also be written, in the absence of specific adsorption, as the sum of the charge and dipole components  

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