The Effect of Stern Layer Thickness on the Diffuse Capacitance for Size Asymmetric Electrolyte inside the Charged Spherical Cavities by Density Functional Theory

Abstract

The Modified Fundamental Measure Theory was used within the Primitive Model to determine Stern layer thickness in charged spherical cavity. The different behaviors for mean electric potential in Stern region with those one in the diffuse region was considered as the best criteria to determine this thickness. Depending on concentration, ion charge and size, and cavity charge the cations or anions may be found at the closest distance from the cavity’s wall, which lead two values for Stern thickness. In the present case study in which anions are assumed to be larger than cations, at zero or low positive values of cavity surface charge, the cations are found at the cavity wall, although the anion’s contact density is larger. But, by increasing the surface charge to a specific level, the cations are repelled away from the wall so that Stern thickness increases and becomes equal to anion radius. It is shown that this specific surface charge decreases not only with anion size, concentration and cation charge but also with rising cavity curvature. Also, we studied that how the diffuse capacitance for size-asymmetric electrolytes is affected by variation in Stern layer thickness.