Does electrical double layer formation lead to salt exclusion or to uptake?

When electric double layers are formed, cases have been reported where this formation involves expulsion of electrolyte into the solution and cases in which electrolyte is absorbed from the solution. Both situations are experimentally and theoretically documented, but they cannot be simultaneously correct. In this paper it is shown that this seeming conflict finds its cause in the way the double layer is formed: expulsion for double layers forming spontaneously by ion adsorption from the solution, but uptake when the double layer is formed by an external field. A thermodynamic analysis is presented.

Figure 1

Trend of the titration charge on oxides for different electrolyte contents.