Diffusion of ionic components in electrolytes not only eliminates the gradients of ionic concentrations but also alters the local dielectric environment, and the coupling effect between kinetic dielectric decrement and ionic concentration gradient on the diffusion dynamics is not well understood. Herein, taking the charging process in electrical double layer systems as a case study, we conduct a multiscale investigation of ion diffusions in aqueous electrolytes by combining the dynamic density functional theory and an ion-concentration-dependent dielectric constant model. By properly considering the time evolutions of local dielectric constant coupled with ion density, we report an interesting phenomenon on the suppression of surface charge density that is not captured by conventional models. In addition, we show that the usage of aqueous electrolyte with small dielectric decrement coefficients promotes the capacitance, in quantitative agreement with experimental measurements.

Using a dynamic density functional theory, we study the charging dynamics, the final equilibrium structure, and the energy storage in an electrical double layer capacitor with nanoscale cathode–anode separation in a slit geometry. We derive a simple expression for the surface charge density that naturally separates the effects of the charge polarization due to the ions from those due to the polarization of the dielectric medium and allows a more intuitive understanding of how the ion distribution within the cell affects the surface charge density. We find that charge neutrality in the half-cell does not hold during the dynamic charging process for any cathode–anode separation, and also does not hold at the final equilibrium state for small separations. Therefore, the charge accumulation in the half-cell in general does not equal the surface charge density. The relationships between the surface charge density and the charge accumulation within the half-cell are systematically investigated by tuning the electrolyte concentration, cathode–anode separation, and applied voltage. For high electrolyte concentrations, we observe charge inversion at which the charge accumulation exceeds the surface charge at special values of the separation. In addition, we find that the energy density has a maximum at intermediate electrolyte concentrations for a high applied voltage.

The adsorption processes of ions into charged nanospace are associated with many practical applications. Whereas a large number of microporous materials have been prepared toward efficient adsorption of ions from solutions, theoretical models that allow for capturing the characteristics of ion dynamic adsorption into like-charged nanopores are still few. The difficulty originates from the overlapping of electric potentials inside the pores. Herein, a theoretical model is proposed by incorporating dynamic density functional theory with modified Poisson equation for investigating the dynamic adsorption of ions into like-charged nanoslits. This model is rationalized by comparing the theoretical predictions with corresponding simulation results. Afterward, by analyzing the adsorption dynamics, we show that the overlapping effect is associated with the pore size, ion bulk concentration, and surface charge density, and it plays a dominant role in the coupling between the total adsorption amount of ions and total adsorption time. Specifically, with weak overlapping effect, the total adsorption amount is intuitively proportional to the total adsorption time; however, when the overlapping effect is strong, the total adsorption amount may be inversely proportional to the total adsorption time, indicating that both high adsorption amount and short adsorption time can be achieved simultaneously. This work provides a meaningful insight toward the rational design and optimization of microporous materials for efficient ion adsorption.

Although ion dehydration in confined water is ubiquitous in many important processes concerning ion adsorption, transport and separation, and so forth, few theoretical models have been developed to unravel the mechanism of dehydration in confined space. Herein, a molecular model is proposed by weighing the molecular ori-

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Many attempts have been made to improve the energy density of supercapacitors toward their large-scale applications in storing renewable energy. Herein, the surface wettability effect is unraveled with the combination of static and dynamic density functional theories through which the energy densities and power densities of electrochemical supercapacitors are analyzed with different sets of pore sizes, surface voltages, and bulk ion concentrations. We demonstrate that tuning the surface wettability of electrodes may improve the energy density but simultaneously reduce the power density, and an optimal energy density with a relatively small cost of power density can be achieved by adopting highly confined pores. In addition, increasing ion bulk concentration and/or surface voltage can enhance both the energy density and power density. This work provides a complementary dynamic insight into the surface wettability effect on the performance of supercapacitors.

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Polymer electrode materials are critical components to achieve the excellent energy storage performance (ESP) of supercapacitors, while the underlying microscopic mechanism by which the polymer structure on the electrode surface affects the energy storage remains unclear. Herein, we explore the effects of a polyelectrolyte (PE) coating on the ESP of supercapacitors by using the polymer density functional theory. The ESP is determined by the adsorption of free ions at the electrode surface, which is jointly affected by the interactions from both the charged surface and the anchored PE chains. Once the PE chains carry like charges as the electrode, the energy density can be significantly promoted by two orders of magnitude. However, if the PE chains carry opposite charges to the electrode, the energy density can be suppressed. The effect of PE coating on the capacitance is similar to that on the energy density if the surface voltage is fixed during the operation, and otherwise, if the surface charge density is fixed, the effect on the capacitance is opposite to that on the energy density. This work provides a microscopic understanding of the complex polyelectrolyte coating’s effects on the ESP in supercapacitors.