Face-to-face heterojunctions within 2D/2D porous NiCo oxyphosphide/g-C₃N₄ towards efficient and stable photocatalytic H₂ evolution

Constructing 2D/2D face-to-face heterojunctions is believed to be an effective strategy to enhance photocatalytic performance due to the enlarged contact interface and increased surface active sites. Herein, 2D porous NiCo oxyphosphide (NiCoOP) was synthesized for the first time and coupled with graphitic carbon nitride (g-C₃N₄) nanosheets to form 2D/2D heterojunctions via an in-situ phosphating method. The optimal 4 wt.% 2D/2D NiCoOP/g-C₃N₄ (OPCN) photocatalyst achieves a hydrogen evolution rate of 1.4 mmol·h⁻¹·g⁻¹, which is 33 times higher than that of pure g-C₃N₄. The greatly improved photocatalytic performance of the composite photocatalysts could be attributed to the formation of interfacial surface bonding states and sufficient charge transfer channels for accelerating carrier separation and transfer and the porous structure of NiCoOP nanosheets with abundant surface active sites for promoting surface reactions. Amazingly, the 2D/2D OPCN composite photocatalysts also exhibit superior stability during photocatalytic reactions. This study not only designs new noble-metal-free NiCoOP/g-C₃N₄ composite photocatalysts but also provides a new sight in fabricating face-to-face 2D/2D heterojunctions for their application in energy conversion areas.