Calculating the Maximum Density of the Surface Packing of Ions in Ionic Liquids

Abstract

The maximum density of monolayer packing on a graphene surface is calculated by means of molecular dynamics (MD) for ions of characteristic size and symmetry: 1-butyl-3-methylimidazolium [BMIM]⁺, tetrabutylammonium [TBA]⁺, tetrafluoroborate [BF4]⁻, dicyanamide [DCA]⁻, and bis(trifluoromethane) sulfonimide [TFSI]⁻. The characteristic orientations of ions in a closely packed monolayer are found. It is shown that the formation of a closely packed monolayer is possible for [DCA]⁻ and [BF4]⁻ anions only at surface charges that exceed the limit of the electrochemical stability of the corresponding ionic liquids. For the [TBA]⁺ cation, a monolayer structure can be observed at the charge of nearly 30 μC/cm² attainable in electrochemical experiment.