Ti3C2Tx Mxenes is an energy storage material with a pseudocapacitive mechanism, which is widely applied in supercapacitors. It is usually prepared by etching Ti3AlC2 with HF or a mixture of HCl and fluoride. However, the Ti3C2Tx Mxenes fabricated by this method have -F terminal groups. The -F groups do not contribute to the energy storage process of the Ti3C2Tx MXenes pseudocapacitance, but also are negative to the charge transfer of the Mxenes and reduces the electrical conductivity. Therefore, how to effectively remove the -F terminal group is the key to the surface engineering of the MXenes. Herein, reductant NaBH4 was proposed to remove the terminal groups of the MXenes. Firstly, Ti3C2Tx Mxenes were prepared by a mixture of HCl and LiF. Then, Mxenes were treated with NaBH4 aqueous solution to remove the surface groups for the preparation of Ti3C2 MXenes. The samples were characterized by XRD, SEM, XPS, and electrochemical workstation. The results showed that the -F terminal group of Ti3C2Tx Mxenes could be removed effectively after NaBH4 treatment, But we also noticed that Mxenes interlayer structure collapse and piled up into pieces due to lack of surface groups, it is bad for ions inserted in the multilayer. Therefore, the multi-walled carbon nanotubes (MWCNTs) were composite to support the multilayer structures before NaBH4 treatment. Ultimately, the eigenimpedance and charge transfer impedance of Ti3C2 Mxenes were decreased significantly. Ti3C2@MWCNTs composite exhibits a high specific capacitance of 257 F g−1 at current density of 1 A g−1 and shows an excellent rate performance. This work provides a method to remove the surface groups of Ti3C2Tx Mxenes, Ti3C2 @MWCNTs demonstrated good electrical conductivity and excellent electrochemical performance. More importantly, specific functional groups can be redecorated for Ti3C2 MXenes on the basis of this work.

Terminal groups of MXenes were removed simply by reduction method to improve the electrochemical performance

ACS Fall 2021

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