Entropy formation of an electrical double layer with divalent off-centre charge cations: Monte Carlo studies

Abstract

Grand canonical Monte Carlo simulations are employed to study the entropy of formation of a planar electric double layer containing equi-sized valency ions. The cation charge is displaced from the ion-sphere centre towards its surface with the displacement being temperature dependent in general, while the monovalent anion charge is held fixed at the centre of the anion sphere. The results for the electrode-ion distributions, the charge density distributions, the differential capacitance, the temperature derivative of the electrode potential, and the entropy of formation of the double layer have been obtained as functions of the electrode charge. For zero cation charge displacement, or for temperature-independent cation charge displacements, a negative temperature dependence of the differential capacitance is observed, while for the temperature-dependent cation charge displacement at negative electrode charges, this temperature dependence can be positive. In the former case, the entropy of formation is negative decreasing on either side of the zero surface charge, while in the latter case the decrease slows down at negative charges reaching positive values at high negative charges. The positive temperature dependence of the differential capacitance is associated with an increase in entropy.