Tailoring Interlayer Structure and Surface Chemical State Intensifies Redox Reaction Activity of Ti3c2tx Mxene

Abstract

MXenes, a new intercalation pseudocapacitive electrode material, stand a chance of enabling high capacitance and high rate for supercapacitor application. However, limited accessible interlayer space and active sites are major challenges to achieve the goal in practical application. Herein, a method of hydrothermal treatment in NaOH solution with reducing reagent-citric acid is firstly proposed to regulate the interlayer environment. As revealed, the interlayer space is expanded and homogenized by Na+ intercalation, which acts as a "expressway" channel to expedite ion diffusion. -F terminations are replaced with O-containing groups, which enhance the hydrophilicity, facilitating electrolyte's accessibility to MXene’s surface and show stronger adsorption of electrolyte ion H+, providing sufficient electrochemical active sites. The change of terminations further leads to the increase in the Ti valence, which becomes more prone to be reduced. The tailoring of interlayer structure and surface chemistry state considerably intensifies the redox reaction activity of MXene, resulting in that H+ is intercalated into the interlays space in a unhydrated form and interacts strongly with O-terminations. Consequently, a pair of clear redox peaks emerge in cyclic voltammograms and a record high capacitance of 543 F/g at 2 mV/s is obtained. This work establishes full knowledge for the rational MXene design for electrochemical energy storage applications.

Keywords: MXene, Redox reaction activity, Supercapacitor, energy storage