Ti3−yNbyC2T MXenes as high-rate and ultra-stable electrode materials for supercapacitors

Despite being a promising supercapacitor electrode material, the development of Ti3C2Tx has still been limited by many obstacles, such as restacking Ti3C2Tx nanosheets and non-electrochemically active fluorine terminations on the surface. Herein, new double transition metal Ti3−yNbyC2Tx MXenes are prepared by etching Ti3−yNbyAlC2 solid solution MAX precursors obtained by self-propagating high-temperature synthesis method for the first time. The synthesized Ti3−yNbyC2Tx MXenes exhibit larger interlayer spacing and more surface -O terminations than Ti3C2Tx, resulting in superior rate performance and high cycling stability as supercapacitors electrode materials. In particular, Ti2.9Nb0.1C2Tx demonstrates a high volumetric specific capacity of 1014 F cm−3 at a scan rate of 2 mV s−1, superior rate performance with a volumetric specific capacity of 422 F cm−3 at a scan rate of 2000 mV s−1, and ultra-long cycling life up to 84000 cycles at a current density of 10 A g−1. This work expands the practical applicability of the MXenes family in energy storage applications and provides a promising strategy to tailor the MXenes interlayer structure and surface chemistry.