Molecular dynamics simulation study of sodium ion structure & dynamics in water in ionic liquids electrolytes using 1-butyl-3-methyl imidazolium tetrafluoroborate and 1-butyl-3-methyl imidazolium hexafluorophosphate.

In this paper, we have performed an all-atom molecular dynamics simulation to understand the structure and dynamics of Na ions in water mixed Ionic liquids (Water in Ionic liquid). Two ionic liquid (IL) systems consist of (1) 1-butyl-3-methylimidazolium [BMIM] tetrafluoroborate [BF] and (2) 1-butyl-3-methylimidazolium [BMIM] hexafluorophosphate [PF] were considered in this work. We understand various intermolecular structures and dynamic and thermodynamic behaviours of Na ions in the watermixed IL systems. The water (HO) mole fractions (x) varied from 0.33 to 0.71. The neat ILs [BMIM][BF] and [BMIM][PF] pairwise radial distribution functions show a decrease with an increase in x. The [BMIM][PF] exhibits a strong coordination structure with Na ions across the entire range of x values. The rdf between the pairs of Na-[PF] presents a significant interaction compared to Na and [BF]. The Na  ions manifested greater coordination with HO In HO-[BMIM][PF] compared to HO-[BMIM][BF]. The self-diffusion coefficient (D) values of Na  ions increase with the rise in x in both ILs. The D values of Na  ions are 10-fold higher in [BMIM][BF] than [BMIM][PF]. The ionic conductivity values are higher for [BMIM][BF]. Overall, this paper unveils molecular-level insights for understanding the behavior of Na ions in the water in ionic liquid systems.