1：Experimental Design and Method Selection:

The study involved synthesizing WO3 films with different crystal facet ratios using hydrothermal and solvothermal methods, followed by loading BiVO4 via spin coating or drop casting to form heterojunctions. The rationale was to explore how facet orientation affects electronic structure and PEC performance. Theoretical models included XRD for crystallographic analysis, UPS and XPS for electronic structure, and PEC measurements for performance evaluation.

2：Sample Selection and Data Sources:

WO3 films were fabricated on FTO substrates with variations in precursor solutions to achieve different facet ratios (e.g., thinflake-WO3, plate-WO3, 200-WO3, 002-WO3). BiVO4 was loaded onto these films. Data sources included synthesized samples characterized by various spectroscopic and microscopic techniques.

3：3). BiVO4 was loaded onto these films. Data sources included synthesized samples characterized by various spectroscopic and microscopic techniques. List of Experimental Equipment and Materials:

3. List of Experimental Equipment and Materials: Chemicals included tungstic acid, sodium tungstate dihydrate, poly(vinyl alcohol), bismuth(III) nitrate pentahydrate, vanadyl acetylacetonate, hydrogen peroxide, oxalic acid, urea, acetonitrile, acetic acid, hydrochloric acid, and deionized water. Equipment included autoclaves for hydrothermal synthesis, spin coaters, furnaces for annealing, XRD instruments (Rigaku Ultima IV, X'PERT PRO), SEM (Quanta 650 FEG), TEM (JEOL 2010 F, EM-002B), UV-vis spectrometer (Cary 5000), XPS (Kratos Axis Ultra), electrochemical workstation (CHI660D), solar simulator (Newport 9600), and oxygen sensor (Fox, Ocean Optics).

4：Experimental Procedures and Operational Workflow:

WO3 films were synthesized via solvothermal or hydrothermal methods with specific precursor compositions and conditions (e.g., temperature, time). BiVO4 was coated by spin coating or drop casting with multiple layers and annealing. Characterization involved XRD, SEM, TEM, XPS, UPS, UV-vis, and PEC measurements in a three-electrode system with Pt counter and Ag/AgCl reference electrodes under AM 1.5 G illumination.

5：5 G illumination. Data Analysis Methods:

5. Data Analysis Methods: Data analysis included calculating intensity ratios from XRD, work function from UPS, band alignments from XPS, photocurrent densities from linear sweep voltammetry, IPCE and APCE from spectral measurements, and faradaic efficiency from oxygen evolution measurements. Statistical techniques were not explicitly mentioned, but software like X'pert texture was used for pole figures.