Voltage-Gated Ionic Conductivity in Ultranarrow Confinement

Voltage-controlled ion transport in subnanometer pores underpins the operation of emerging filtration, energy-storage, and iontronic technologies, yet its microscopic mechanisms remain poorly understood. Using classical molecular dynamics simulations, we investigate ionic transport in ultranarrow (≤1 nm) quasi-two-dimensional nanopores in MXene electrodes filled with an ionic liquid. We reveal a nonmonotonic dependence of linear-response conductivity on electrode potential, with a pronounced asymmetry between positive and negative electrode polarizations. These behaviors originate from a competition between confinement-induced ionic ordering and charging-induced ion crowding within the pore. The resulting transition from a structure-limited to an ion-crowding-limited transport regime provides a general framework for understanding voltage-gated ionic conduction under extreme confinement, which facilitates the formulation of design principles for MXene-based nanofluidic, electrochemical, and iontronic devices.