Densification of Ionic Liquid Molecules within a Hierarchical Nanoporous Carbon Structure Revealed by Small-Angle Scattering and Molecular Dynamics Simulation

Abstract

The molecular-scale properties of the room temperature ionic liquid (RTIL) 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl) imide, [C4mim+][Tf2N–], confined in nanometer-scale carbon pores have been investigated using small-angle X-ray and neutron scattering and fully atomistic molecular dynamics simulations. [C4mim+][Tf2N–] densities significantly higher than that of the bulk fluid at the same temperature and pressure result from the strong affinity of the RTIL cation with the carbon surface during the initial filling of slitlike, subnanometer micropores along the mesopore surfaces. Subsequent filling of cylindrical ∼8 nm mesopores in the mesoporous carbon matrix is accompanied by weak RTIL densification. The relative size of the micropores compared to the ion dimension, and the strong interaction between the RTIL and the slit-like micropore, disrupt the bulk RTIL structure. This results in a low-excluded volume, high-RTIL ion density configuration. The observed interfacial phenomena are simulated using a molecular dynamics model consisting of a linear combination of mesopore and micropore effects. These observations highlight the importance of including the effects of a porous substrate’s internal surface morphology, especially roughness and microporosity, on the resulting electrolyte structural properties and performance in electrical energy storage applications.

Efficient storage mechanisms for building better supercapacitors

“…In contrast, Bañuelos et al combined SANS and molecular dynamics simulations to investigate the adsorption of a roomtemperature ionic liquid (RTIL) inside a hierarchical porous carbon at various loadings 28 and concluded that the RTIL covers the pore surfaces uniformly, rather than leaving some pore surfaces unsaturated. eir pictures of the wetting of mesopores and micropores are shown in Fig.…”

Nanoporous carbon for electrochemical capacitive energy storage

“…Besides, ion confinement in carbon micropores has also been studied with SAXS. 203 By combining in situ SAXS and Monte Carlo simulation the degree of confinement (DoC) of ions in micropores has been reported for an aqueous-based electrolyte. 128 Fig.…”

“…293 Afterwards, the arrangement of ions in carbon micropores and mesopores was studied with various combinations of ionic liquids. 43,203,[294][295][296][297][298] The greatest advantage of MD simulation is the possibility of modeling the charging dynamics in nanopores. As shown in the previous section, there are mainly three charging mechanisms: counter-ion adsorption, co-ion desorption, and ion exchange.…”

“…Some experimental works, including basic electrochemical analysis and in situ techniques, such as in situ EQCM, in situ NMR, in situ SAXS, and simulation method at the molecular level, delivered some insights such as mentioned earlier. 203,228,284,294,296,332,[364][365][366] The information of how ions are packed inside nanopores, the selectivity of ions, and the charging mechanisms in such an electrolyte system will hopefully help to develop porous materials with the optimized structure to boost the performance of EDLCs.…”

Room temperature ionic liquids: A simple model. Effect of chain length and size of intermolecular potential on critical temperature

“…8 The conductivity has been measured 9 for two different RTILs doped with lithium. Other area of interest is the behavior of imidazolium-based RTIL in the presence of nanoporous carbon or nanostructures [10][11][12] to produce electrical double layer capacitors. Simulations on chiral RTIL, 13 calculation of acoustic modes, 14 and study of structure stability of proteins dissolved in RTIL 15 have also been performed.…”