Transport of room-temperature ionic liquids in nanopores under external electric fields

Room-temperature ionic liquids (RTILs) are promising electrolytes that are composed entirely of ions but are liquid at room temperature. Their remarkable properties such as wide electrochemical window make them ideal electrolytes in many electrochemical systems. Here, using molecular dynamics simulations, we studied transport of RTILs in conical nanopores under external electric fields. The current through the pores was found to increase nonlinearly as applied voltage increases. The nonlinearity was traced back to that the RTILs’ electrical conductivity increases as the magnitude of the electric field increases and as the ion concentration decreases. At the same applied voltage, the current through the nonuniformly charged pore was weaker than that through the neutral pore, while the current through the uniformly charged pore was stronger. This is because the hindered transport due to the higher total ion concentration and the lower degree of ion depletion dominates in the nonuniform case, while the enhanced transport due to the formation of electrical double layers dominates in the uniform case. Physical insights provided in this study demonstrate the importance of solvent-free nature and strong ion–ion correlations in RTILs on their nonequilibrium transport in nanopores.