1：Experimental Design and Method Selection:

The study involves synthesizing WO3 nanoparticles via sol-gel method, depositing them on TCO substrates using spray-coating, and annealing with different heating ramps (fast and slow) to optimize photoelectrochemical performance. Theoretical models include Williamson-Hall analysis for XRD peak broadening.

2：Sample Selection and Data Sources:

Samples are prepared with varying deposition volumes (20-120 mL) leading to different film thicknesses (0.26-5.5 μm). Data sources include photoelectrochemical measurements, SEM, XRD, and UV-vis spectroscopy.

3：26-5 μm). Data sources include photoelectrochemical measurements, SEM, XRD, and UV-vis spectroscopy. List of Experimental Equipment and Materials:

3. List of Experimental Equipment and Materials: Equipment includes a spray-coating gun (Wuto-7902-BL), furnace for annealing, photoelectrochemical cell (cappuccino cell), ZENNIUM workstation (Zahner Elektrik), solar simulator (Oriel, Newport), SEM (FEI Quanta 400FEG), XRD (Rigaku SmartLab), and profilometer (Dektak XT, Bruker). Materials include tungsten powder, hydrogen peroxide, TCO glass substrates, methanesulfonic acid electrolyte, and reference/counter electrodes.

4：Experimental Procedures and Operational Workflow:

WO3 nanoparticles are synthesized, dispersed in water/ethanol, spray-coated on heated TCO substrates, annealed at 550°C for 1 hour with different ramps, and characterized for morphology, structure, and photoelectrochemical performance using j-V curves, SEM, XRD, and UV-vis.

5：Data Analysis Methods:

Data analysis involves ImageJ for SEM image processing, Williamson-Hall analysis for crystallite size and microstrain from XRD, Tauc plot for band gap determination, and statistical comparison of photocurrent densities.