Thickness-Independent Capacitive Performance of Holey Ti 3 C 2 T x Film Prepared through a Mild Oxidation Strategy.

The Ti 3 C 2 T x film with metallic conductivity and high pseudo-capacitance holds profound promise in flexible high-rate supercapacitors. However, the restacking of Ti 3 C 2 T x sheets hinders ion access to thick film electrodes. Herein, a mild yet green route has been developed to partially oxidize Ti 3 C 2 T x to TiO 2 /Ti 3 C 2 T x by introducing O 2  molecules during refluxing the Ti 3 C 2 T x suspension. The subsequent etching away of these TiO 2  nanoparticles by HF leaves behind numerous in-plane nanopores on the Ti 3 C 2 T x sheets. Electrochemical impedance spectroscopy shows that longer oxidation time of 40 min yields holey Ti 3 C 2 T x (H-Ti 3 C 2 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 pristineTi 3 C 2 T x film (75.58 s). Meanwhile, H-Ti 3 C 2 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 Ti 3 C 2 T x film. The method reported herein would pave way for fabricating porous MXene materials toward high-rate flexible supercapacitor applications.