Two-dimensional Ti3C2 MXene nanosheets were synthesized by selective etching of Al layer from ternary carbides Ti3AlC2 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 Ti3C2 MXene were investigated. With longer etching time, Ti3C2 nanosheets were gradually delaminated and more C was exposed. The electrochemical properties of Ti3C2 show a significant improvement at the reaction time of 216 h (Ti3C2-216), with no obvious changes with etching time from 2 to 168 h. Ti3C2-216 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. (C) 2016 The Electrochemical Society. All rights reserved.