Insight into Manipulation Mechanism of Ion Transport through Angstrom-Scale Channels in Ti3C2Tx Membrane by Controlling Surface Potential Using Electrochemical Quartz Crystal Microbalance with Dissipation

A lamellar membrane assembled by parallel restacking of two-dimensional nanosheets provides a novel platform for studying the electrostatic manipulation of ion mobility under angstrom-scale confinement. The membrane nanostructure in aqueous solution is unstable due to intercalation. However, because accurate measurements of structural changes under different charged conditions are difficult, their effect on the ion modulation was seldom fully addressed, and the electrostatic modulation mechanism was not good. Here, we report the efficient manipulation of ion diffusion in the confined channels through a Ti3C2Tx membrane and gain insight into the mechanism by an in situ measurement of the lamellar nanostructure using an electrochemical quartz crystal microbalance with dissipation (EQCM-D). By precisely tuning the external potential directly applied to the membrane, the ion permeation rate can be effectively and reversibly increased by 6 times or decreased by 15 times. The EQCM-D measurement provides empirical evidence to demonstrate that the anomalous ion-flow modulation is determined by both the channel diameter and an ion rearrangement in the electrical double layers (EDLs), particularly, in the Stern layers. Although the channel expanded at low negative voltage, the ion permeation rate decelerated due to the counterion distribution in the Stern layers.