1：Experimental Design and Method Selection:

The study utilized a simple and cost-effective simultaneous and sequential cation and/or anion doping technique to mono-dope and co-dope the TiO2 nanotubes. The nanotubes were grown using electrochemical anodization techniques with tunable length, diameter, and wall thickness by control of the applied voltage, growing time, and electrolyte composition.

2：Sample Selection and Data Sources:

Undoped and doped TiO2 nanotube membranes were fabricated. The doping was achieved using precursor-charged electrolyte for anion doping or polarity-switching technique for cation doping.

3：List of Experimental Equipment and Materials:

A two-electrode system with a titanium foil as the anode, a platinum sheet as the cathode, and fluoride-based non-aqueous electrolyte was used for nanotube growth. Field emission SEM (JEOL JSM-7401F) was used for morphology and structure analysis. UV–vis spectra were characterized with a VWR UV-1600PC spectrophotometer. Electrochemical characterizations were performed with a Bio-logic SP-200 potentiostat.

4：Experimental Procedures and Operational Workflow:

Nanotube growing was processed under constant voltage (30 V) condition for three hours. Simultaneous anion doping was conducted by adding correspondent precursors into the electrolyte. A voltage switching technique was used for cation doping. All samples were annealed at 500 °C for 2 h in an ambient atmosphere before further characterization.

5：Data Analysis Methods:

The performance of the undoped/doped TiO2 nanotubes in solar energy to chemical fuel conversion was evaluated using wired and wireless configurations. Photocurrent and IPCE measurements were conducted to study the photoresponse of these nanotubes with different energy photon excitation.