Achieving High Pseudocapacitance of 2D Titanium Carbide (MXene) by Cation Intercalation and Surface Modification

Supercapacitors attract great interest because of the increasing and urgent demand for environment‐friendly high‐power energy sources. Ti 3 C 2 , a member of MXene family, is a promising electrode material for supercapacitors owing to its excellent chemical and physical properties. However, the highest gravimetric capacitance of the MXene‐based electrodes is still relatively low (245 F g −1 ) and the key challenge to improve this is to exploit more pseudocapacitance by increasing the active site concentration. Here, a method to significantly improve the gravimetric capacitance of Ti 3 C 2 T x MXenes by cation intercalation and surface modification is reported. After K + intercalation and terminal groups (OH − /F − ) removing , the intercalation pseudocapacitance is three times higher than the pristine MXene, and MXene sheets exhibit a significant enhancement (about 211% of the origin) in the gravimetric capacitance (517 F g −1 at a discharge rate of 1 A g −1 ). Moreover, the as‐prepared electrodes show above 99% retention over 10 000 cycles. This improved electrochemical performance is attributed to the large interlayer voids of Ti 3 C 2 and lowest terminated surface group concentration. This study demonstrates a new strategy applicable to other MXenes (Ti 2 CT x , Nb 2 CT x , etc.) in maximizing their potential applications in energy storage.