1：Experimental Design and Method Selection:

A facile solvothermal method was used to synthesize white TiO2 nanosheets, followed by a solid-phase NaBH4 reduction method to produce black TiO2 ? x nanosheets under moderate temperature.

2：Sample Selection and Data Sources:

Samples were prepared using hydrofluoric acid and titanium butoxide for solvothermal synthesis, and sodium borohydride for reduction.

3：List of Experimental Equipment and Materials:

Equipment includes Teflon-lined stainless steel autoclave, horizontal tube furnace, Bruker D8 Advance XRD, JEM1400plus TEM, SPI3800/SPA400 AFM, PHI 5000 VersaProbe XPS, Lambda 750 UV/Vis/NIR spectrometer, FTIR spectrometer, Bruker EMX-10/12 EPR, Micrometrics ASAP 2020 analyzer, Neware BTS-5 V 50 mA battery tester, CEL-SPH2N photocatalytic system, CEL-PF300-T8 xenon arc lamp, GC7920-TF2Z gas chromatograph. Materials include HF, TBOT, NaBH4, N2 gas, HCl, ethanol, water, graphite, PVDF binder, NMP solvent, Cu foil, LiPF6 electrolyte, EC/DMC mixture.

4：Experimental Procedures and Operational Workflow:

For TiO2 NS synthesis, HF was added to TBOT, stirred, autoclaved at 190°C for 24h, centrifuged, washed with ethanol, dried. For TiO2 ? x NS, NaBH4 and TiO2 NS were ground, heated at 300°C under N2 for 1h, stirred in HCl, washed, dried. Characterizations included XRD, TEM, HR-TEM, AFM, XPS, UV-Vis-NIR DRS, FTIR, EPR, N2 sorption. Electrochemical tests used CR2025 cells with active material, graphite, PVDF on Cu foil, tested with Neware device. Photocatalytic tests used

5：5 mg sample in water under visible light from xenon lamp with UV-cutoff filter, H2 analyzed by GC. Data Analysis Methods:

Data were analyzed using instrument-specific software for XRD, TEM, XPS, etc.; electrochemical data analyzed for capacity and cycling performance; photocatalytic data analyzed for H2 production rates.