The Electrical Double Layer as a Capacitor. Evaluation of Capacitance in Different Solutions: Effect of Ion Concentrations, Sizes, and Valencies

Realistic applications of CDLE require a proper analysis of the effect of the different ionic species existing in natural waters. Here we focus on the role of specificity of ions, particularly, in multiionic solutions. With this purpose, a model is presented in which electric double-layer (EDL) overlapping and the existence of a Stern layer are considered. It is also taken into account that ions can be tightly packed by using the Carnahan-Starling model. This model is applied to analyze the structure of the EDL with multiionic solutions containing divalent ions. Other models are briefly discussed, including modified Donnan model, in which the micropores are envisaged as homogeneously charged charge reservoirs. Finally, the consequences on the CDLE cycle is briefly commented.