Hierarchical Co₃(PO₄)₂/CuI/g-CH₂ S-Scheme Heterojunction for Efficient Photocatalytic Hydrogen Evolution

Graphdiyne (GD), a new type of carbon allotrope formed by sp and sp² hybrid carbon atoms, has attracted wide attention due to its high π-conjugation degree, special band structure, and uniformly distributed pores. In traditional synthesis methods, hexaethylbenzene was coupled on the substrate catalytic material (copper foil or foamed copper) to generate graphdiyne. In this work, CuI was used as the substrate catalytic material, and the CuI-GD composite was synthesized by cross-coupling in the pyridine solution of hexaethylbenzene. For the first time, Co₃(PO₄)₂ was modified by the CuI-GD composite material to prepare a Co₃(PO₄)₂/CuI-GD S-scheme heterojunction catalyst, which avoided the complicated process of removing the substrate catalytic material. Under the action of the internal electric field, electrons are induced to move quickly and directionally, and the powerful photogenerated electrons in the conduction band (CB) of GD and the holes in the valence band (VB) of CuI are retained to participate in the photocatalytic reaction. These advantages were combined with the high-energy acetylene bond in GD, which accelerated the catalytic reaction of the Co₃(PO₄)₂/CuI-GD heterostructure. Electrochemical and fluorescence analysis showed that Co₃(PO₄)₂/CuI-GD has faster electron and hole separation efficiency, lower hydrogen evolution overpotential, and higher carrier utilization. Therefore, Co₃(PO₄)₂/CuI-GD exhibited good hydrogen evolution activity. This work shows that GD has broad prospects in designing high-performance photocatalyst systems.