Impact of Sodium Fluorosulfonyl(trifluoromethylsulfonyl)amide Salt on Interfacial Ordering of 1-Methyl-1-Propylpyrrolidinium Fluorosulfonyl(trifluoromethylsulfonyl)amide Ionic Liquid near Graphite Electrodes at Different Applied Potentials.

In this study, constant potential molecular dynamics simulations have been employed to investigate the impact of sodium fluorosulfonyl(trifluoromethylsulfonyl)amide (NaFTA) salt on the interfacial properties of 1-methyl-1-propylpyrrolidinium fluorosulfonyl(trifluoromethylsulfonyl)amide (Pyrr1,3FTA) ionic liquid (IL) confined between two graphite electrodes at different applied potential differences. For the pure IL, it is observed that at higher negative voltages, the FTA- anions are completely replaced by Pyrr1,3 + cations, resulting in an unsolvated cation near the negative electrode. In the salt-IL solutions, at 0.1 mole fraction of the salt, most of the Na+ ions are found to interact with the FTA- near the positive electrode, and a moderate presence of Na+ ions is observed closer to the negative electrode. Interestingly, accumulation of Na+ ions near both the electrodes is observed in the solution having highest mole fraction of the salt (xNaFTA = 0.3). A nonmonotonous change in the intensity of the peaks in the number density profile of the Na+ ions is observed near the positive electrode surface. Analysis of the average orientational order parameter for the Pyrr1,3 + cations reveals a parallel arrangement of their ring closer to the negative electrode, which is minimally affected by the presence of NaFTA salt. The distribution of the C-S-S-F improper dihedral angle of the FTA- ions near the positive electrode (+2.5 V) interfacial region shows that the probability of finding their g a u c h e $g a u c h e$ conformation increases up to 0.2 mole fraction of the salt.