Mechanisms and effects of gas intercalation into ionic liquids confined within charged nanoscale volumes

Abstract

Understanding the behavior of gas within confined ionic liquids (ILs) is important for a wide range of emerging energy, separation, and sensing technologies. However, the mechanisms governing gas solubility and molecular structure within these systems remain largely unknown. Here, we investigate the factors that dictate the intercalation and arrangement of CO₂, N₂ and O₂, in a commonly used IL (1-butyl-3-methylimidazolium hexafluorophosphate, [BMIM⁺][PF₆⁻]) confined within neutral and charged 2.1 nm diameter carbon nanotubes (CNTs) via molecular dynamics simulations and enhanced free energy sampling methods. Our simulations show that the gas selectivity in these systems can be explained by a competitive complex interplay between confinement, charge state of CNTs, and IL properties. We then experimentally validate a subset of these predictions using a novel device consisting of electrically addressable, IL-infilled CNTs which we expose to CO₂ and O₂ in a N₂ background. Our findings help to disentangle the relative importance of tuning gas solubility and preferential proximity to the CNT wall for maximizing measurable changes of electrochemical signals. These insights provide a foundation for engineering future electrochemical systems utilized in gas sensing or separation applications.