Fig. 1. Fabrication process of TiO₂/Ti₃C₂T_x heterostructure on a flexible substrate.

Step 1: MXene (Ti₃C₂T_x, crystal structures in the left panel, is drawn by Vesta software) aerogel is obtained by freeze drying of the Ti₃C₂T_x nanosheets dispersion and the derived TiO₂ aerogel is obtained by annealing the MXene aerogel in air at 400 °C. Step 2: Ti₃C₂T_x and TiO₂ 2D nanosheets are dispersed, respectively, in IPA, injected into the interface between hexene and DI water, and self-assembled into nanometer-thick Ti₃C₂T_x and TiO₂ films. Step 3: the thin films are transferred onto a flexible substrate (e.g., PET) in a layer-by-layer fashion to realize the TiO₂/MXene heterostructure, where the TiO₂ layer serves as the electrochromic component, and the MXene layer serves as the transparent electrode.