Highlight on H-Bond Interaction-Associated Multiple Ion Layer Formation of an Imidazolium-Based Ionic Liquid on a Potential-Bias Surface: Molecular Dynamics Simulations

Abstract

Multiple ion layer formation associated with molecular orientation alteration and hydrogen bonding in a supercapacitor model with 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([C2mim][NtF2]) as a room-temperature ionic liquid (RTIL) electrolyte has been investigated using potential-bias classical molecular dynamics (CMD) simulations. A 50-ion pair model was used to observe the molecular ion layer formation of [C2mim][NtF2] of the simulated electrified graphite electrode. After applying the potential bias, multiple layers of [C2mim]+ and [NtF2]- formed and became more pronounced. An orientation analysis indicated that the higher potential differences play a significant role in [C2mim]+, especially near the negative surface. The π-πstacking interaction between [C2mim]+ rings and graphene electrodes was clearly perceived. Principal component analysis (PCA) was introduced to address the characteristics of the layer formation, respectively, to the potential bias applied to the simulated model. PCA scores from the applied potential (ΔE = 0.0, 1.0, 2.0, 3.0, and 4.0 V) were used to group the characteristics of the atom pairing associated with the number of H-bonds between H atoms in the [C2mim]+ cation and all atoms in the [NtF2]- anion.