1：Experimental Design and Method Selection:

A facile and inexpensive approach to produce highly stable and 2.6 wt.% atomically dispersed Ni atoms on nitrogen-doped graphene (Ni-NG) by a routine wet impregnation method, followed by an NH3 treatment process. The prepared Ni-NG sample was coupled with CdS semiconductor photocatalyst and employed as a new and active non-noble metal cocatalyst for PHE reactions.

2：6 wt.% atomically dispersed Ni atoms on nitrogen-doped graphene (Ni-NG) by a routine wet impregnation method, followed by an NH3 treatment process. The prepared Ni-NG sample was coupled with CdS semiconductor photocatalyst and employed as a new and active non-noble metal cocatalyst for PHE reactions. Sample Selection and Data Sources:

2. Sample Selection and Data Sources: Graphene oxide (GO) was synthesized using a modified Hummer method. Single Ni atoms anchored N-doped graphene (Ni-NG) was prepared using an impregnation method followed by an NH3 treating process.

3：List of Experimental Equipment and Materials:

Transmission electron microscopy (TEM), high-angle annular dark field (HAADF) scanning transmission electron microscopy (STEM), field emission scanning electron microscopy (FESEM), energy-dispersive X-ray spectroscopy (EDS) mapping, X-ray diffraction (XRD), XPS analyses, fluorescence spectrum, time-resolved photoluminescence (TRPL) decay spectra, Raman spectra, elemental analyses using a 5100 Agilent Inductively Coupled Plasma Spectrometry (ICP).

4：Experimental Procedures and Operational Workflow:

Photocatalytic hydrogen reactions were carried out in a 20 mL flask at ambient temperature. Fabricated photocatalyst samples (5.0 mg) were dispersed into 10 mL 1.0 M aqueous (NH4)2SO3 solution and sonicated for several minutes. Prior to visible light irradiation, the solution was degassed with N2 gas for 2 hours to remove dissolved oxygen. A 300 W Xe lamp equipped with a UV light filter (λ > 420 nm) was employed as a visible light source.

5：0 mg) were dispersed into 10 mL 0 M aqueous (NH4)2SO3 solution and sonicated for several minutes. Prior to visible light irradiation, the solution was degassed with N2 gas for 2 hours to remove dissolved oxygen. A 300 W Xe lamp equipped with a UV light filter (λ > 420 nm) was employed as a visible light source. Data Analysis Methods:

5. Data Analysis Methods: The evolved H2 was analyzed by a gas chromatograph (Techcomp Limited Co., GC 7890-II) with a thermal conductivity detector. Ultra pure nitrogen was used as a carrier gas.