Insight into the Electrical Double Layer of an Ionic Liquid on Graphene

Abstract

Graphene is a promising next-generation conducting material with the potential to replace traditional electrode materials in supercapacitors. Since energy storage in supercapacitors relies on the electrolyte-electrode interface, here we elucidate the interfacial subnanometer structure of a single component liquid composed solely of cations and anions – an ionic liquid- on electrified graphene. We study the effect of applied potential on the interaction between graphene and a silicon tip in an ionic liquid and describe it within the framework of the Derjaguin-Landau-Verwey-Overbeck (DLVO) theory. The energy is stored in an electrical double layer composed of an extended Stern layer, which consists of multiple ion layers over ~2 nanometers, beyond which a diffuse layer forms to compensate the applied potential on graphene. The electrical double layer significantly responds to the applied potential, and it shows the transition from overscreening to crowding of counterions at the interface at the highest applied potentials. It is proposed that surface charging occurs through the adsorption of the imidazolium cation to unbiased graphene (likely due to π-π interactions) and that the surface potential is better compensated when counterion crowding happens. This study scrutinizes the electrified graphene-ionic liquid interface, with implications not only in the field of energy storage, but also in lubrication.

Nanoporous carbon for electrochemical capacitive energy storage

“…However, as an ideal 2D carbon surface, graphene offers great opportunities as a model surface material to develop some fundamental studies on the understanding of EDL formation in real and simulation experiments. 93…”

Atomic Force Spectroscopy on Ionic Liquids

“…The conclusions derived from the simulation closely match the experimental results, showing the versatility of AFS for investigating the electric double layer in ionic liquids. Jurado et al [102] extended the investigations of carbon-based materials to the graphene surface. They investigated the interface formed with [EMIm][TFSI] at zero charge as well as under applied potential, concluding that the strong interaction of the imidazolium ring with the graphene surface via π-π bonding results in a preferential orientation of the ions and to an overscreening, even on the uncharged surface.…”

Atomistic Insight into the Electrochemical Double Layer of Choline Chloride–Urea Deep Eutectic Solvents: Clustered Interfacial Structuring

“…reported both experimentally and computationally. 8,48,49 In summary, atomistic molecular dynamics have been used to simulate the electrical double layer structure of choline chloride-urea in 1:2 molar ratio (Reline) on a graphene electrode.…”