Enhanced Capacitive Performance Based on Diverse Layered Structure of Two-Dimensional Ti₃C₂MXene with Long Etching Time

Two-dimensional Ti 3 C 2 MXene nanosheets were synthesized by selective etching of Al layer from ternary carbides Ti 3 AlC 2 MAX phase using HF solution for different etching times and then evaluated as working electrodes. The effects of the etching time on the morphology, structure, surface termination, and electrochemical properties of Ti 3 C 2 MXene were investigated. With longer etching time, Ti 3 C 2 nanosheets were gradually delaminated and more C was exposed. The electrochemical properties of Ti 3 C 2 show a significant improvement at the reaction time of 216 h (Ti 3 C 2 -216), with no obvious changes with etching time from 2 to 168 h. Ti 3 C 2 -216 exhibited higher capacitive performance with the specific capacitance of 118 F g −1 at the scan rate of 5 mV s −1 , excellent rate performance, and cycling stability. This improvement in the performance is attributed to higher carbon content for better conductivity and faster transportation of electrons, and the larger specific surface area for more access of aqueous electrolyte to the electrodes.