1：Experimental Design and Method Selection:

The study used aerosol pyrolysis (AP) for depositing Sn-doped hematite films on various substrates (FTO, Ti, stainless steel) and employed dip coating and spray pyrolysis for TiO2 capping to enhance stability. Photoelectrochemical measurements were conducted to assess performance and photocorrosion resistance.

2：Sample Selection and Data Sources:

Substrates included FTO/glass (TCO22-15, Solaronix), Ti sheet (Alfa Aesar 99.7%), and stainless steel (17248). Precursors were FeCl3 and SnCl2 for hematite, and titanium isopropoxide or titanium di-isopropoxide bis-acetylacetonate for TiO

3：7%), and stainless steel (17248). Precursors were FeCl3 and SnCl2 for hematite, and titanium isopropoxide or titanium di-isopropoxide bis-acetylacetonate for TiOList of Experimental Equipment and Materials:

2. 3. List of Experimental Equipment and Materials: Equipment included X-ray diffractometer (X'pert Philips MPD), FE-SEM (Hitachi SEM FE 4800), UV-Vis spectrometers (Cary 100 Conc, Mikropack NanoCalc 2000), optical microscope (Axio Scope A1, Zeiss), ICP-OES (Optima 8000, Perkin Elmer), potentiostat (Voltalab 10 PGZ-100), photocurrent spectra system (CIMPS-pcs, Zahner), solar simulator (150 W Xe arc lamp, Newport), lasers, and photodiode (S1337-1010BQ, Hamamatsu). Materials included chemicals from Sigma-Aldrich, Fluka, Penta, and Alfa Aesar.

4：Experimental Procedures and Operational Workflow:

Films were deposited by AP at 450-700°C, with TiO2 coatings applied via dip coating (annealed at 500°C) or spray pyrolysis (at 450°C). Characterization involved XRD, SEM, UV-Vis, and ICP analysis. Photoelectrochemical tests were performed in H2SO4 or NaOH electrolytes under illumination, with IPCE and polarization curves measured.

5：Data Analysis Methods:

Data were analyzed using software like VoltaMaster 4 for potentiostat control, and ICP for iron concentration determination. Statistical analysis was not explicitly mentioned, but results were compared across samples.