Ionic Liquids under Confinement: From Systematic Variations of the Ion and Pore Sizes toward an Understanding of the Structure and Dynamics in Complex Porous Carbons

Abstract

We use molecular simulations of an ionic liquid in contact with a range of nanoporous carbons to investigatecorrelations between the ion size, pore size, pore topology, and properties of the adsorbed ions. We show that diffusioncoefficients increase with the anion size and, surprisingly, with the quantity of adsorbed ions. Bothfindings are interpreted interms of confinement: when the in-pore population increases, additional ions are located in less-confined sites and diffuse faster.Simulations in which the pores are enlarged while keeping the topology constant support these observations. The interpretationof properties across structures is more challenging. An interesting point is that smaller pores do not necessarily lead to a largerconfinement. In this work, the highest degrees of confinement are observed for intermediate pore sizes. We also show acorrelation between the quantity of adsorbed ions and the ratio between the maximum pore diameter and the pore limitingdiameter.