Highly efficient nitrogen fixation over S-scheme heterojunction photocatalysts with enhanced active hydrogen supply

Photocatalytic N₂ fixation is a promising strategy for ammonia (NH₃) synthesis; however, it suffers from relatively low ammonia yield due to the difficulty in the design of photocatalysts with both high charge transfer efficiency and desirable N₂ adsorption/activation capability. Herein, an S-scheme CoS_x/ZnS heterojunction with dual active sites is designed as an efficient N₂ fixation photocatalyst. The CoS_x/ZnS heterojunction exhibits a unique pocket-like nanostructure with small ZnS nanocrystals adhered on a single-hole CoS_x hollow dodecahedron. Within the heterojunction, the electronic interaction between ZnS and CoS_x creates electron-deficient Zn sites with enhanced N₂ chemisorption and electron-sufficient Co sites with active hydrogen supply for N₂ hydrogenation, cooperatively reducing the energy barrier for N₂ activation. In combination with the promoted photogenerated electron-hole separation of the S-scheme heterojunction and facilitated mass transfer by the pocket-like nanostructure, an excellent N₂ fixation performance with a high NH₃ yield of 1175.37 μmol g^-1 h^-1 is achieved. This study provides new insights into the design of heterojunction photocatalysts for N₂ fixation.