2D Carbide MXene under postetch low-temperature annealing for high–performance supercapacitor electrode

MXene, as an emerging class of conductive two-dimensional materials, have extraordinary applications in the field of electrochemical energy storage. However, the intrisic capacity of MXene still need to be improved due to the large gap to their theoretical capacity. Here, we provide a facile and new strategy to enhance their electrochemical performance—postetch low-temperature annealing (below 400 °C) under Ar atmosphere. Due to the formation of more C-Ti-O active sites and larger interlayer voids, the Ti₃C₂T_x freestanding film annealed under 200 °C exhibits a high capacitance of 429 F/g and energy density of 29.2 Wh/Kg in 1 M H₂SO₄ electrolyte, it could withstand 5000 cycles with 89% of the capacitance retention. By comparison, the Ti₃C₂T_x annealed at higher temperature (400 °C), presented a high resistance and poor electrochemical property because of partial oxidation and breaking of Ti-C bond on the surface of MXene nanosheets, despite the larger interlayer voids and low –F contents,. This work is not only probing the importance to maintain the original structure of MXene but also proposing a new strategy to realizing a high capacitance of pure MXene electrode.