*2.3. Characterisation*

SEM images were measured on FEI Verious 460 L scanning electron microscope (Hillsboro, OH, USA). AFM images were investigated by Icon Bruker microscope (Ettlingen, Germany). TEM images were measured on a FEI Tecnai G2F20 S-TWIN microscope equipped with an energy-dispersive spectrometer (EDS) (Hillsboro, OH, USA). XPS analysis were measured on a Thermo ESCALAB 250 spectrometer (Shanghai, China). The EC and capacitive properties of the films were determined by combining the in-situ TU-1901 PERSEE UV-vis spectrophotometer (Beijing, China) with an CHI660B Chenhua electrochemical workstation (Shanghai, China) in a three-electrode configuration, where the nanocomposites served as the working electrodes; a Pt plate/Pt wire acted as the counter electrode, and Ag/AgCl was used as the reference electrode.

**Figure 1.** Characterization of material preparation process. (**a**) Schematic outline of the fabrication process of nanocomposite film; (**b**) UV-vis absorption spectra of composite film on quartz substrate (number of cycles: 2–16). Inset: plots of the absorbance values at 201 and 289 nm as a function of the layer number.

#### **3. Results and Discussion**
