1：Experimental Design and Method Selection:

A solvothermal method was used to synthesize Ni-doped Zn0.5Cd0.5S catalysts. Photocatalytic tests for hydrogen evolution and selective oxidation were conducted under visible light irradiation. Photoelectrochemical tests and computational methods (DFT with CASTEP) were employed to analyze charge separation and electronic properties.

2：5Cd5S catalysts. Photocatalytic tests for hydrogen evolution and selective oxidation were conducted under visible light irradiation. Photoelectrochemical tests and computational methods (DFT with CASTEP) were employed to analyze charge separation and electronic properties. Sample Selection and Data Sources:

2. Sample Selection and Data Sources: Samples included pure Zn0.5Cd0.5S and Ni-ZCS with varying Ni doping percentages (1-7%). Materials were purchased from Sinopharm Chemical Reagent Co., Ltd., Aladdin Chemical Reagent Co., Ltd., and Alfa Aesar Chemical Co., Ltd.

3：5Cd5S and Ni-ZCS with varying Ni doping percentages (1-7%). Materials were purchased from Sinopharm Chemical Reagent Co., Ltd., Aladdin Chemical Reagent Co., Ltd., and Alfa Aesar Chemical Co., Ltd. List of Experimental Equipment and Materials:

3. List of Experimental Equipment and Materials: Equipment included TEM (TECNAI G2 F20, FEI), FE-SEM (Ultra Plus, Carl Zeiss), XRD (Bruker D8), UV–vis spectrophotometer (PuXinTU-1901), XPS (PHI5702), PEC system (CHI-660D), LED lamp (CEL-LED 100), gas chromatography (GC 9560), fluorescence spectrophotometer (Hitachi FL-4500), ESR spectrometer (JES-FA 200, Bruker). Materials included Ni(CH3COO)2·4H2O, Cd(NO3)2·4H2O, Zn(NO3)2·6H2O, (NH4)2S, ethanol, methanol, Na2S, Na2SO3, benzyl alcohol, and others.

4：Experimental Procedures and Operational Workflow:

Synthesis involved dissolving metal salts in ethanol, adding (NH4)2S, heating in an autoclave at 180°C for 24h, washing, and drying. Photocatalytic tests were done in a reactor with catalyst dispersed in Na2S/Na2SO3 solution under Xe lamp irradiation. H2 evolution was measured by GC. Electrodes were prepared on FTO glasses for PEC tests. Computational geometry optimization and DOS calculations were performed.

5：Data Analysis Methods:

Data analysis included using Debye-Scherrer's formula for particle size, Nernst equation for potential conversion, and statistical analysis of photocatalytic rates and efficiencies.