Mo₂C was synthesized by a high temperature solid state method using ammonium molybdate ((NH₄)₆Mo₇O₂₄·4H₂O) and dicyanodiamine (C₂H₄N₄) as raw

materials, then Mo₂C/ZnIn₂S₄ composite was prepared by in-situ growth method. The composition, structure and properties of the materials were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), UV-vis diffuse reflection (UV-vis) and Kelvin probe (KP). The results show that ZnIn₂S₄ grows in-situ on the surface of Mo₂C particles and forms Mo₂C/ZnIn₂S₄ heterojunctions. The hydrogen evolution rate of Mo₂C/ZnIn₂S₄ composite reaches 1.33 mmol/g/h, which is 5.1 times to that of bare ZnIn₂S₄. The photocatalytic mechanism analysis shows that Mo₂C, as a cocatalyst, has metallic properties, high conductivity and high surface work function. After Mo₂C/ZnIn₂S₄ heterogeneous interface formed between Mo₂C and ZnIn₂S₄, the Mo₂C/ZnIn₂S₄ composite can effectively promote the separation and migration rate of photogenerated charges in ZnIn₂S₄. Meanwhile, Mo₂C becomes the active site of hydrogen evolution reaction due to its low hydrogen evolution overpotential, which effectively reduces the overpotential of ZnIn₂S₄ in hydrogen evolution reaction, and subsequently improves the photocatalytic hydrogen evolution activity of the composite material.