Thickness-Independent Capacitive Performance of Holey Ti₃C₂T_x Film Prepared through a Mild Oxidation Strategy

Abstract

The Ti3C2Tx film with metallic conductivity and high pseudo-capacitance holds profound promise in flexible high-rate supercapacitors. However, the restacking of Ti3C2Tx sheets hinders ion access to thick film electrodes. Herein, a mild yet green route has been developed to partially oxidize Ti3C2Tx to TiO2/Ti3C2Tx by introducing O2 molecules during refluxing the Ti3C2Tx suspension. The subsequent etching away of these TiO2 nanoparticles by HF leaves behind numerous in-plane nanopores on the Ti3C2Tx sheets. Electrochemical impedance spectroscopy shows that longer oxidation time of 40 min yields holey Ti3C2Tx (H-Ti3C2Tx) 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 pristineTi3C2Tx film (75.58 s). Meanwhile, H-Ti3C2Tx 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 Ti3C2Tx film. The method reported herein would pave way for fabricating porous MXene materials toward high-rate flexible supercapacitor applications.