The electrical double layer is a structure that describes the variation of electric potential near a surface, and has a large bearing on the behaviour of colloids and other surfaces in contact with solutions and solid state fast ion conductors. The analogue in a plasma is the double layer.
Later Gouy and Chapman (1910-1913) made significant improvements by introducing a diffuse model of the electrical double layer, in which the potential at a surface decreases exponentially due to adsorbed counter-ions from the solution.
The current classical electrical double layer is the Gouy-Chapman-Stern model, which combines the Helmholtz single adsorbed layer with the Gouy-Chapman diffuse layer. Important approximations used in this model are:
Classical models of electrical double layer are not suited for the fast ion conductor/metal interface as the concentration of mobile ions in solid ion conductor can be extremely high, Ni~1022/cm3.