1：Experimental Design and Method Selection

The study employed a combination of modified Hummer method, dip-coating method, and chemical vapor deposition (CVD) technique for the preparation of G/R-GO/CNT photoelectrode.

2：Sample Selection and Data Sources

Graphite powder, graphene oxide (GO), and carbon nanotubes (CNTs) were used as primary materials. The exhaust car solution was used as the electrolyte for water splitting experiments.

3：List of Experimental Equipment and Materials

Graphite (VEB Laborchemie Apolda, Germany), H2SO4, H3PO4, DMF (Sigma-Aldrich), NaOH, acetone, Commercial C2H4 gas, H2O2, KMnO4 (Adwic Company, Egypt), field emission scanning electron microscope (ZEISS SUPRA 55 VP, Gemini Column), X-ray diffractometer (PANalytical X'Pert Pro, Holland), double beam spectrophotometer (PerkinElmer, Lamba 950), micro Raman spectroscopy (Bruker, Germany).

4：Experimental Procedures and Operational Workflow

1. Preparation of R-GO using modified Hummer method. 2. Coating of R-GO on graphite electrode using dip-coating method. 3. Preparation of CNTs on G/R-GO electrode using CVD technique. 4. Characterization of the prepared materials using XRD, FESEM, HRTEM, and Raman analyses. 5. Photoelectrochemical water splitting experiments using G/R-GO/CNT electrode under artificial light.

5：Data Analysis Methods

Optical band gaps were calculated using Tauc's equation. Photoelectrochemical performance was evaluated based on current density and incident photon-to-current efficiency (IPCE). Thermodynamic parameters were calculated using Arrhenius and Eyring equations.