1：Experimental Design and Method Selection:

A facile, one-pot hydrothermal method was used to synthesize Cu2O/TiO2 p-n heterojunction composites with AOT surfactant to control morphology and enhance photocatalytic activity.

2：Sample Selection and Data Sources:

Cubic Cu2O particles and TiO2 nanoparticles were synthesized; composites with different TiO2 mass ratios (

3：5 wt.%, 25 wt.%, 50 wt.%, 60 wt.%, 80 wt.%) were prepared. List of Experimental Equipment and Materials:

Chemicals included cupric acetate, sodium citrate dihydrate, ascorbic acid, sodium hydrate, titanium tetrachloride, AOT surfactant, normal butanol, absolute ethyl alcohol; equipment included Teflon-lined autoclaves, XRD (Bruker D8), SEM (JSM-7001F), TEM (JEM-2100), HRTEM, BET (Belsorp-mini II), XPS (Thermo Fisher Scientific), UV-vis spectrophotometer (UV-U3900), PL spectrophotometer (F-7000), electrochemical workstation (CHI660D), gas chromatograph (Agilent 7890A).

4：Experimental Procedures and Operational Workflow:

Synthesis involved hydrothermal reactions at specific temperatures and times; characterization included XRD, SEM, TEM, BET, XPS, UV-vis, PL, EIS, photoelectrochemical measurements; photocatalytic activity was evaluated in a closed system with a Xe lamp and methanol sacrificial reagent.

5：Data Analysis Methods:

Data were analyzed using standard techniques for XRD peak identification, BET surface area calculation, UV-vis band gap estimation, PL intensity comparison, EIS Nyquist plot fitting, and GC quantification of H2 production.