MXenes are attracting growing attentions from scientific community owing to their decent electric and ionic conductivity, highly accessible surface area, and the presence of redox-active sites. Herein, an acid molecular scissor is proposed to artificially tailor Ti3CNTx MXene at the atomic scale and create defective nanosheets and redox-active sites. The tailored Ti3CNTx MXene exhibits a significantly improved electrochemical performance with the specific capacitance reaching 376 F g?? 1 and 230.68 mF cm?? 2, much higher than that of original Ti3CNTx MXene (237 F g?? 1 and 168.27 mF cm?? 2). The tailored Ti3CNTx MXene was further assembled into a microsupercapacitor, which demonstrates a high volumetric capacitance of 250 F cm?? 3, a high energy density of 12.46 mW h cm?? 3 at a power density of 0.43 W cm?? 3. This work offers a new strategy to reinvent MXenes at the atomic scale with largely enhanced redox-active sites for energy storage, catalysis, solid lubricants and electromagnetic interference shielding.