(591e) Time-Dependent Density Functional Theory for Ion Transport in Room-Temperature Ionic Liquids

Understanding the charging kinetics of electric double layers (EDLs) is of fundamental significance importance for the design and development of novel electrochemical Nano-devices such as supercapacitors and field-effect transistors. In this work, we study the dynamic behavior of room-temperature ionic liquids (RTILs) using a classical time-dependent density functional theory (TD-DFT) which that accounts for the molecular excluded volume effects and electrostatic correlations to study the dynamic process of charging and discharging of EDLs in ionic liquid. Our theoretical results for the charging and discharging of EDLs show that the counterintuitive charging kinetics in ionic liquids is closely affiliated with the local segregation of counterions and co-ions near the electrode surface, leading to formation of layer-by-layer ionic densities. We also find that the charging and discharging are symmetrical processes, the surface charge density for the charging and the discharging both follow the exponential decay. While an equivalent circuit (EC) model predicts a monotonic increase of the surface charge upon application of an electrode voltage, TDDFT predicts three types of charging behavior depending on the system geometry and the surface electrical potential.