Dual Near-Infrared-Response S-Scheme Heterojunction with Asymmetric Adsorption Sites for Enhanced Nitrogen Photoreduction

Photocatalytic nitrogen reduction reaction (PNRR) holds immense promise for sustainable ammonia (NH₃) synthesis. However, few photocatalysts can utilize NIR light that carries over 50% of the solar energy for NH₃ production with high performance. Herein, a dual NIR-responsive S-scheme ZnCoS_x/Fe₃S₄ heterojunction photocatalyst is designed with asymmetric adsorption sites and excellent PNRR performance. The heterojunction possesses a hollow-on-hollow superstructure: Fe₃S₄ nanocrystal-modified ZnCoS_x nanocages as building blocks assemble into spindle-shaped particles with a spindle-like cavity. Both Fe₃S₄ and ZnCoS_x are NIR active, allowing efficient utilization of full-spectrum light. Moreover, an S-scheme heterojunction is constructed that promotes charge separation. In addition, the Fe/Co dual-metal sites at the interface enable an asymmetric side-on adsorption mode of N₂, favoring the polarization and activation of N₂ molecules. In combination with the promoted mass transfer and active site exposure of hollow superstructure, a superior PNRR performance is achieved, with a high NH₃ evolution rate of 2523.4 µmol g^-1 h^-1, an apparent quantum yield of 9.4% at 400 nm and 8% at 1000 nm, and a solar-to-chemical conversion efficiency of 0.32%. The work paves the way for the rational design of advanced heterojunction catalysts for PNRR.