Flow-induced voltage generation by driving imidazolium-based ionic liquids over a graphene nano-channel

Abstract

Inspired by the interesting phenomenon that biological systems have the inherent skill to generate significant bioelectricity when the salt content in fluids flows over highly selective ion channels on cell membranes, in this study, the flow-induced voltage is investigated by driving the pure bulk room-temperature ionic liquid (RTIL) 1-ethyl-3-methylimidazolium tetrafluoroborate ([Emim][BF₄]) flowing over a graphene nano-channel consisting of two parallel single-layered graphene sheets using molecular dynamics simulation for the first time. Considering the combined effect of cations and anions in the adsorbed layer on the free charge carriers of the graphene surfaces (the interactions are 12.0 and 7.0 kJ mol⁻¹ per cation/anion and graphene, respectively) and the characteristic of Coulomb's law, we have developed an advanced equation that can effectively and accurately calculate the flow-induced voltage of RTIL and graphene nano-channel system on the nano-scale. A maximum flow-induced voltage of 2.3 μV is obtained from this nano-scaled system because the free charge carrier on the graphene channel surfaces is dragged along the pure bulk RTIL's direction of movement. A saturation of the flow-induced voltage with increased flow velocity is observed, and this saturation can be attributed to the balance between the external driving force and viscous resistance arising from the internal RTIL and graphene nano-channel. Further analysis shows that the flow-induced voltages gradually increase towards saturation from 1.9 to 2.1 μV or decrease from 2.3 to 2.1 μV when the distance between the two parallel single-layered graphene or the area of single-layered graphene of the nano-channel increases from 1 to 5 nm or from 1 to 25 nm², respectively. Additionally, the influence of the system temperature (viscosity) and average flow velocity on the flow-induced voltage is investigated.