Non-Coulombic Structure of Ionic Liquid Confined in Carbon Micropores with HR MC-Aided X-Ray Scattering

 

We applied the HRMC simulation-aided X-ray scattering for elucidation of the 3D structure of  ionic liquid of 1-ethyl-3-methylimidazolium bis(trifluorometanesulfonyl) imide (EMI-TFSI) confined in nanopores of carbide-derived carbons of 0.7 nm and 1.0 nm in width. We analyzed the plausible anion-anion, cation-cation, and anion-cation structures using the corresponding electron radial distribution functions obtained from the HRMC. We found the unprecedented accumulation of co-ions in the first coordination shell of EMI-TFSI in the nanopores, although the co-ions in the first coordination shell should be highly repulsive electrostatically. The occupation percents of anions around an anion in 0.7 nm-pores and in bulk liquid are 23 % and 7 %, respectively.  The unusual accumulation of co-ions cannot be understand by Coulomb’s law. The high accumulation of co-ions at the first coordination shell can be ascribed to the creation of image charges in the electrical conductive carbon walls.