Approximate analytical expressions for the properties of an electrical double layer with asymmetric electrolytes

Abstract

Approximate analytical expressions for the electrostatic potential distribution, surface excess of co-ion, and double-layer Helmholtz energy and entropy for flat surfaces are derived. The present analysis extends the Göuy–Chapman formula in that asymmetric electrolytes are considered. The mathematical treatment of the Poisson–Boltzmann equation is based on an assumed semi-empirical fourth-order polynomial function with parameter k, which is a measure of the degree of asymmetry of the electrolytes. The results of numerical simulation reveal that the deviation of the present approximate result from the corresponding exact value for the double-layer properties under consideration is ca. 5%.