▎ 摘 要
Ioniccurrent rectification (ICR) in nanofluidic diodes is determinedby a combination of channel geometry and surface charge, where mostof the previous works have focused on charged asymmetric channels.In this work, through a series of molecular dynamics simulations,we find a surprising ICR phenomenon in a Janus graphene channel, whosegeometry is symmetric, while the surface charge is asymmetric by tuningthe ratio of cationic and anionic surface modification. A key observationis that when the electric field changes from positive to negativedirection, the ionic current exhibits a switchable on-off statedepending on whether the dipole moment of the channel's innersurface is parallel to the electrical force. Strikingly, the ICR ratioshows a maximum behavior with the increase in cationic modification,attributed to the change in the range of electrostatic repulsion underthe negative electric field. Furthermore, for a given modificationratio, with the increase in graphene layer distance, the ICR ratioalso displays a maximum behavior because of the reduced range of theelectric double layer (EDL). For small layer distance, the EDL overlapleads to a Coulomb blockade effect under the positive electric field,corresponding to a small ionic current. However, the large layer distancereduces the influence of EDL on ion transport owing to the weakenedelectrostatic interactions, which ultimately leads to the decreasein ICR ratio. Our results shed light on the essential role of chargepolarity in ICR performance, which could open a new window for thedesign of novel nanofluidic diodes based on symmetric Janus channels.