Enhanced ion transport in nanochannels of MXenes by Mg2+ pre-intercalation

Abstract

How to enhance the ion transport between MXene layers is a critical topic in the fields of electrochemical storage (especially supercapacitors) and water treatment. Vertical structure design of MXene nanosheets and single-molecule organic pre-intercalation are proposed, but the methods to enhance the ion transport through MXene nanochannels by modulating MXene's surface state have not been investigated yet. The interaction mechanism between Mg²⁺ and MXene 2D nanochannels during the transport process has not been thoroughly explored. In our work, we used a facile infiltration method to immerse the Ti₃C₂T_x membranes in MgCl₂ solution for ion pre-intercalation. We found that the pre-intercalation of Mg²⁺ has a significant effect on the increase of the ion transport rate of Ti₃C₂T_x membranes, especially for Li⁺ which reached 268.49% compared with those of non-intercalation membranes. Through multiple characterization methods, we discovered that the enhancement of ion transport rate by pre-intercalation of Mg²⁺ mainly originated from the fact that the pre-intercalation of Mg²⁺ increased the layer spacing of MXene films as the channel support between layers while Mg²⁺ increased the work function (WF) of 2D nanochannels thereby reducing the interaction of other ions with the channel surface. The acceleration phenomenon of ion transport by surface state modulation proposed in our work will provide new strategies for the design of structure and regulation of surface states, revealing the mechanism of capacity improvement.