Multi-ionic effects on the equilibrium and dynamic properties of electric double layers based on the Bikerman correction

Abstract

Multi-ion electrolytes are used in many electrochemical applications; therefore, systematic analyses of the effect of multi-ion electrolytes on the capacitance and charging rate are required. In this study, the electrochemical behaviors of the electrical double layer of multi-ion electrolytes confined between parallel electrodes are predicted using a continuum approach. To study the characteristics of multi-ion electrolytes, modified Poisson?Boltzmann equations and modified Poisson?Nernst?Planck equations with the Bikerman correction term were used. Multi-valence and multisize ion electrolytes with various compositions were selected, and the ion distribution, capacitance, and charging rates were obtained. We divided fluxes into thermal, electrical, and Bikerman-type fluxes for further investigation. In multi-valence cases, a relatively small number of high-valence ions might significantly enhance the equilibrium capacitance. However, the small number of the ions restricts the system from reaching equilibrium. In multi-size cases, smaller ions enhance the equilibrium capacitance, and the curves for the capacitance and charging rates gradually change as the fraction of the smaller ions increases. The results of this study should provide strategies for modifying the capacitance and charging rates using multi-ion electrolytes.