1：Experimental Design and Method Selection:

A sol-gel methodology was used to synthesize single-phase BiFeO3 film on TiO2 photoanode. The design rationale was to utilize ferroelectric polarization to enhance charge separation and light absorption.

2：Sample Selection and Data Sources:

FTO substrates were used, cleaned ultrasonically. TiO2 films were synthesized by spin-coating from a sol-gel solution. BFO films were synthesized with different thicknesses (3, 5, 8 times coating) and annealed.

3：List of Experimental Equipment and Materials:

Equipment includes ultrasonic cleaner, oven, spin coater, Muffle furnace, X-ray diffractometer (Miniflex 600), scanning electron microscope (FEI Apreo), high-resolution transmission electron microscope (GATAN 832), X-ray photoelectron spectrometer (Kratos AXIS Ultra DLD), UV-Vis spectrophotometer (Shimadzu MPC-3100), fluorescence spectrophotometer (Shimadzu RF-5300PC), Xe lamp, three-electrode configuration with Pt sheet and SCE reference electrode. Materials include FTO substrates, acetone, ethanol, DI water, anhydrous ethanol, titanium isopropoxide, hydrochloric acid, Fe(NO3)3·9H2O, Bi(NO3)3·5H2O, citric acid, ethylene glycol, epoxy resin, 1M NaOH aqueous solution.

4：Experimental Procedures and Operational Workflow:

Clean FTO substrates, synthesize TiO2 films by spin-coating and annealing at 500°C. Prepare BFO precursor solution, coat and pre-anneal at 300°C, repeat for thickness control, final anneal at 500°C. Conduct poling experiments with ±5V. Characterize with XRD, SEM, HRTEM, XPS, UV-Vis DRS, PL. Perform PEC measurements in three-electrode cell under dark, visible light, and AM

5：5V. Characterize with XRD, SEM, HRTEM, XPS, UV-Vis DRS, PL. Perform PEC measurements in three-electrode cell under dark, visible light, and AM5G illumination, measure EIS and Mott-Schottky plots. Data Analysis Methods:

1.5G illumination, measure EIS and Mott-Schottky plots. 5. Data Analysis Methods: XRD for crystal structure, SEM and HRTEM for morphology, XPS for chemical composition, UV-Vis for absorption, PL for carrier recombination, J-V curves for photocurrent density, EIS for charge transfer resistance, Mott-Schottky for carrier density calculation using equation Nd = 2 / (e0 * ε * ε0 * k).