1：Experimental Design and Method Selection:

The study used a direct impregnation-calcination method to deposit CdO nanoparticles into TiO2 nanotube structures. TiO2 nanotubes were prepared via an optimized two-step anodization process. Characterization methods included SEM, TEM, UV-Vis DRS, XPS, XRD, and PEC measurements to analyze morphology, crystallinity, composition, and photoelectrochemical properties.

2：Sample Selection and Data Sources:

Titanium foil samples (0.1×30×40 mm, 99.6+% purity) were used. CdO-TiO2 nanotubes were prepared with varying concentrations of cadmium nitrate tetrahydrate (10, 30, 50, 70, 200, and 800 mM).

3：1×30×40 mm, 6+% purity) were used. CdO-TiO2 nanotubes were prepared with varying concentrations of cadmium nitrate tetrahydrate (10, 30, 50, 70, 200, and 800 mM). List of Experimental Equipment and Materials:

3. List of Experimental Equipment and Materials: Equipment included a ZEISS-IGMA HD/VP SEM, D/max-2200PC XRD, AXIS Ultra XPS, JEM-2100 TEM, UV-2550 UV-Vis spectrophotometer, AUTOLAB PGSTAT 30 for impedance-potential measurements, and Optimax 365 UV light source. Materials included titanium foil, ethylene glycol, deionized water, citric acid, ammonium fluoride, cadmium nitrate tetrahydrate, and sodium sulfate electrolyte.

4：Experimental Procedures and Operational Workflow:

TiO2 nanotubes were prepared by degreasing Ti foil, anodizing in a two-electrode system with specific electrolyte and conditions, followed by UV irradiation and immersion in Cd(NO3)2 solutions at different concentrations, rinsing, drying, and annealing at 450°C. PEC measurements used a three-electrode setup with CdO/TiO2 as working electrode, platinum net as counter electrode, and Ag/AgCl as reference electrode in 1 M Na2SO4 electrolyte under nitrogen purging.

5：Data Analysis Methods:

Data were analyzed using techniques such as XRD for phase identification, XPS for chemical composition, Mott-Schottky plots for flatband potential and charge carrier density calculation, and IPCE calculation from photocurrent measurements.