In situ oxygen doped Ti₃C₂T_x MXene flexible film as supercapacitor electrode

Heteroatom doping has been proven to be an effective strategy to improve the electrochemical energy storage capacity of two-dimensional MXenes. However, the heteroatom for MXenes is mainly focused on the N atoms, while the effects and underlying mechanisms of O substituted partial C atoms of MXene have not been explored so far. Herein, comprehensive research is firstly performed to reveal the oxygen doping mechanism in Ti₃C₂T_x MXene by the experimental characterization and the density functional theory simulation. The in situ oxygen doped Ti₃C₂T_x nanosheets, in which oxygen atoms substitute partial carbon atoms in the titanium octahedron, are synthesized by etching the oxygen doped Ti₃AlC₂ MAX phase, which is more facile than the complex post-doped process. The introduction of appropriate oxygen atoms can effectively improve the interlayer space, electronic conductivity, and interface charge transfer of the Ti₃C₂T_x MXene as a supercapacitor electrode. Further, the electrochemical performances demonstrate that the oxygen doped MXene (O-Ti₃C₂T_x-0.05) film electrode can deliver a higher capacity of 306.0 C g⁻¹ compared to the pristine Ti₃C₂T_x electrode (216.8 C g⁻¹). Besides, the quantitative analysis results imply that the enhanced capacitance is mainly attributed to the diffusion-controlled capacitance and interface capacitance, which result from the higher Ti metal active center, the enhanced quantum capacitance, and the higher adsorption energy.