Thickness‐Independent Capacitive Performance of Holey Ti₃C₂T<i>_x</i> Film Prepared through a Mild Oxidation Strategy

Abstract

The Ti₃ C₂ T_x film with metallic conductivity and high pseudo-capacitance holds profound promise in flexible high-rate supercapacitors. However, the restacking of Ti₃ C₂ T_x sheets hinders ion access to thick film electrodes. Herein, a mild yet green route has been developed to partially oxidize Ti₃ C₂ T_x to TiO₂ /Ti₃ C₂ T_x by introducing O₂ molecules during refluxing the Ti₃ C₂ T_x suspension. The subsequent etching away of these TiO₂ nanoparticles by HF leaves behind numerous in-plane nanopores on the Ti₃ C₂ T_x sheets. Electrochemical impedance spectroscopy shows that longer oxidation time of 40 min yields holey Ti₃ C₂ T_x (H-Ti₃ C₂ T_x ) with a much shorter relax time constant of 0.85 s at electrode thickness of 25 µm, which is 89 times smaller than that of the pristineTi₃ C₂ T_x film (75.58 s). Meanwhile, H-Ti₃ C₂ T_x film with 25 min oxidation exhibits less-dependent capacitive performance in film thickness range of 10-84 µm (1.63-6.41 mg cm^-2 ) and maintains around 60% capacitance as the current density increases from 1 to 50 A g^-1 . The findings clearly demonstrate that in-plane nanopores not only provide more electrochemically active sites, but also offer numerous pathways for rapid ion impregnation across the thick Ti₃ C₂ T_x film. The method reported herein would pave way for fabricating porous MXene materials toward high-rate flexible supercapacitor applications.