Structural analysis of an amino acid ionic liquid: Bulk and electrical double layer

The interfacial structures and macroscopic properties of electrical double layer for 1-ethyl-3-methyl-imidazolium phenyl alanine ([EMIM][PHE]), as an amino acid ionic liquid (AAIL), have been investigated by molecular dynamics simulation and compared with conventional [EMIM][PF6] IL. Results of bulk state showed that hydrogen atoms of ring in [EMIM]+ are capable to form hydrogen bond with the nitrogen and oxygen of [PHE]−. The number of these hydrogen bonds enhances if IL is introduced to graphene sheet. Surprisingly, it was observed that anion-anion hydrogen bond is also probable for [EMIM][PHE]. Introducing the AAIL to graphene does not affect number of this anion-anion hydrogen bond. Being in touch with graphene or not, the main correlation regime between anion and cation is the tail-ring for studied systems. It was observed that phenyl ring of [PHE]− acts as an inhibitor for [EMIM]+ to form π-π stacking with graphene. This behavior leads to higher accumulation of [PHE]− than [EMIM]+ in the first layer. In the current study, a responding electrical potential for an assumed supercapacitor was also introduced. Responding potential of [EMIM][PHE] is lower than [EMIM][PF6].