Nanocrystallization of Imidazolium Ionic Liquid in Carbon Nanotubes

Room-temperature ionic liquids (ILs) have been of considerable worldwide interest as universal solvents, reaction media, gas scavengers, and electrolytes, particularly in supercapacitors. The behavior of ILs confined in nanoscale cavities is essential for high-performance capacitors, yet it is not well understood. Here, the structural properties of the 1-ethyl-3-methylimidazolium chloride IL confined in small diameter carbon nanotubes (CNTs) are characterized by experimental structural and vibrational analyses, complemented by molecular simulations. The IL poorly fills the 1 nm CNTs and the included IL possesses a similar local structure to that seen in the bulk. For 2 and 3 nm diameter CNTs, highly ordered cationic networks associated with restricted vibrational motion are observed. Anions are relatively mobile in the ordered cationic network within the CNTs. Rigid crystalline cationic networks and mobile chloride anions distinguish the unique properties of the confined IL.