1：Experimental Design and Method Selection:

The study involved preparing solid solutions via solid-state reaction, characterizing materials using XRD, UV-vis-NIR spectroscopy, SEM, and DFT calculations, and evaluating photocatalytic and photoelectrochemical performances.

2：Sample Selection and Data Sources:

Samples included Cu3MS4 (M=V, Nb, Ta) and their solid solutions Cu3Nb1-xVxS4 and Cu3Ta1-xVxS4, prepared with specific stoichiometries.

3：List of Experimental Equipment and Materials:

Equipment included X-ray diffractometer (Rigaku MiniFlex), UV-vis-NIR spectrometer (Jasco V-570), SEM (Jeol JSM-6700F), potentiostat (Hokuto Denko HZ-5000 and HZ-7000), gas chromatograph (Shimadzu GC-8A), light sources (300W Xe lamp, solar simulator), and materials like CuS, V2S3, NbS4, TaS2, RuCl3, K2SO3, Na2S.

4：2S. Experimental Procedures and Operational Workflow:

4. Experimental Procedures and Operational Workflow: Preparation involved mixing starting materials, sealing in quartz ampules, calcining, drop-casting for electrodes, loading cocatalysts, and conducting H2 evolution and photoelectrochemical measurements under controlled conditions.

5：Data Analysis Methods:

Data analyzed using DFT calculations for band structures, Kubelka-Munk method for spectra, and gas chromatography for H2 quantification.