1：Experimental Design and Method Selection:

A facile hydrothermal method was used to synthesize Nb-doped WO3 nanotriangle thin films on FTO substrates. The process involved condensation of peroxopolytungstic acid solution containing Nb precursor at 150°C, followed by annealing at 500°C. This method allowed simultaneous doping and thin film formation in a single step.

2：Sample Selection and Data Sources:

Undoped and Nb-doped WO3 thin films were synthesized. The amount of niobium(V) ethoxide was varied to achieve different doping levels, with 2.12 at% Nb identified as optimal based on EDS analysis.

3：12 at% Nb identified as optimal based on EDS analysis. List of Experimental Equipment and Materials:

3. List of Experimental Equipment and Materials: Materials included sodium tungstate dihydrate (Na2WO4·H2O, Junsei ≥99.0%), hydrochloric acid (HCl, Sigma Aldrich), hydrogen peroxide (H2O2, Sigma Aldrich), niobium(V) ethoxide (Nb[OCH2CH3]5, Sigma Aldrich 99.95%), and FTO substrates. Equipment included SEM (Hitachi S4800), XRD (MiniFlex), TEM (JEOL JEM-2100F), UV-Vis spectrophotometer (Varian Cary 5000), XPS (Thermo Fisher Scientific), electrochemical analyzer (Iviumstat), solar simulator (ABET Technologies Sun 2000), and monochromator (Thermo Oriel Cornerstone 7400 1/8).

4：0%), hydrochloric acid (HCl, Sigma Aldrich), hydrogen peroxide (H2O2, Sigma Aldrich), niobium(V) ethoxide (Nb[OCH2CH3]5, Sigma Aldrich 95%), and FTO substrates. Equipment included SEM (Hitachi S4800), XRD (MiniFlex), TEM (JEOL JEM-2100F), UV-Vis spectrophotometer (Varian Cary 5000), XPS (Thermo Fisher Scientific), electrochemical analyzer (Iviumstat), solar simulator (ABET Technologies Sun 2000), and monochromator (Thermo Oriel Cornerstone 7400 1/8). Experimental Procedures and Operational Workflow:

4. Experimental Procedures and Operational Workflow: PTA solution was prepared by adding HCl and H2O2 to sodium tungstate solution. Nb precursor was added, and the mixture was hydrothermally condensed at 150°C for 2.5 hours. After synthesis, films were rinsed and annealed at 500°C for 2 hours. PEC measurements were conducted in a three-electrode setup with 0.5 M Na2SO4 electrolyte under AM 1.5G illumination.

5：5 hours. After synthesis, films were rinsed and annealed at 500°C for 2 hours. PEC measurements were conducted in a three-electrode setup with 5 M Na2SO4 electrolyte under AM 5G illumination. Data Analysis Methods:

5. Data Analysis Methods: Data were analyzed using techniques such as XRD for crystallography, SEM/TEM for morphology, UV-Vis for optical properties, XPS for surface composition, LSV for photocurrent, IPCE for efficiency, EIS for impedance, and Mott-Schottky analysis for carrier density and flat band potential.