The facile synthesis of layered Ti2C MXene/carbon nanotube composite paper with enhanced electrochemical properties.

Ti2AlC has been investigated for several decades, but much less attention has been paid to its delamination and potential energy storage applications, mainly due to the difficulty of delamination and its oxidation features. Herein, a new path to enhance exfoliation and delamination of two-dimensional (2D) Ti2CTx MXene is used. By using an etchant of HCl + LiF, multilayer Ti2CTx is easy to obtain. With only the assistance of mild sonication for 1.5 h without any additional intercalation, two-dimensional (2D) Ti2CTx flake suspensions are produced. Subsequently, the as-fabricated stable suspensions of delaminated Ti2CTx flakes are combined with carbon nanotubes. After filtration, a two-dimensional layered Ti2CTx/carbon nanotube (CNT) nanocomposite "paper" is prepared. Owing to the larger specific area of MXene flakes, which is caused by the complete exfoliation of MXene, with carbon nanotubes assisting with structural support between layers to prevent restacking, this structure provides a rapid charge transfer path during electrochemical reactions. When the nanocomposite paper is used as a lithium ion battery anode, it exhibits a higher capacitance and better cycling stability (a reversible capacity of 155.5 mA h g-1 at 100 mA g-1 after 200 cycles). Moreover, the "paper" can be directly used for electrodes in supercapacitors; the calculated capacitances are 515.3 F g-1 and 694 F cm-3 at a scanning rate of 2 mV s-1. The facile synthesis of layered Ti2C MXene/carbon nanotube nanocomposite paper provides a more secure and easy way to fabricate promising energy storage materials, and creates wider opportunities for exploiting the potential of other MXenes.