(190j) Structural and Dynamical Properties of the Ionic Liquid [BMIM+][PF6-] Confined Inside a Graphitic Slit Pore

A fundamental understanding of the behavior of ionic liquids (ILs) confined in nanopores is necessary to explore and optimize applications in electrochemical double-layer capacitors (EDLCs) and dye-sensitized solar cells (DSSCs).

In this work we have used molecular simulation to investigate the structural and dynamical properties of the IL [BMIM⁺][PF₆^-] when confined inside a slit-like graphitic pore. Different structural properties (local density profiles, order parameters) and dynamical properties [mean squared displacements (MSDs) in different directions, van Hove correlation functions and intermediate scattering functions] were determined for the confined IL. Our results suggest that the local dynamics of the ions depend strongly on their position inside the pore. Close to the pore walls, the typical relaxation times are larger than those for the ions in the center of the pore. Cations have faster relaxation times than anions everywhere in the system. Important spatial heterogeneities in the dynamics of the confined IL are observed, and those are compared against results observed for the same IL in bulk systems at the same temperatures. The dynamics of the confined ions is one important factor that determines the internal resistance in an EDLC, which ultimately affects its specific power (i.e., how quickly an EDLC can deliver energy).