*3.3. Photoelectrochemical Measurements*

Various electrochemical techniques such as cyclic voltammetry (CV), chronoamperometry (CAM) and electrochemical impedance spectroscopy (EIS) were performed to evaluate the photoelectric properties of the prepared composites. Electrodes of the prepared powder materials were first prepared over fluorine-doped tin oxide (FTO) substrate using the dropcasting technique. A slurry of the powder materials and isopropanol solvent was prepared via ultrasonication. 50 μL was withdrawn and uniformly deposited over FTO substrate, and this step is repeated three times while the amount of the powder was controlled to be 4 mg over an area of ca. 1 cm2. Then the electrodes were dried naturally at room temperature without any posttreatment. A rectangular quartz cell (50 mL capacity) with a three-electrode cell configuration was employed in the measurements, where a platinum wire was used as the counter electrode, sat. Ag/AgCl electrode was used as reference electrode and FTO act as the working electrode. All three electrodes were immersed in a dissolved air-free electrolyte of 0.1M Na2SO4 (purge with Ar gas) then connected to the electrochemical workstation (CS350, CorrTest Instruments, Wuhan, China). UV-LED (25 W, 365 nm, NVMUR020A, NICHIA, Japan) was used as a light source in the chronoamperometry test. Multiple cyclic voltammetry was measured with a scan rate of 50 mV/s and potential window from −1.0 to 1.0 V. Chronoamperometry was performed for 660 s at a fixed potential of 0.6 V. Electrochemical impedance spectroscopy (EIS) measurement was conducted at 20 mV amplitude with a frequency range from 10<sup>5</sup> to 0.01 Hz under dark conditions.
