Synergistic Fe ₄ S ₄ /Fe ₂ S ₂ Dual‐Active Sites Enable Sacrificial‐Agent‐Free Photocatalytic Ammonia Synthesis with Solar‐Driven Fertilizer Applications

Photocatalytic nitrogen reduction to ammonia (NH₃) under ambient conditions offers a sustainable alternative to the energy-intensive Haber-Bosch process but faces significant challenges. Inspired by biological nitrogen fixation, a thiosalicylic acid (TSA)-derived Fe-S cluster catalyst with dual active sites (Fe₄S₄ and Fe₂S₂) is rationally designed and synthesized. Guided by the hard-soft acid-base (HSAB) theory, the Fe²⁺/Fe³⁺ ratio in the iron source is optimized to regulate the content of these two coordination structures in the catalysts. Experiments and theoretical calculations reveal that Fe₄S₄ exhibits strong N₂ adsorption energy and enhances charge carrier mobility, while Fe₂S₂, with a higher d-band center, significantly reduces the reaction energy barrier and enhances the reducing capability. The synergistic effect of these dual Fe-S clusters endows the catalyst with exceptional photocatalytic performance, achieving a remarkable NH₃ production rate of 1287.6 µmol h^-1 g^-1 under air without sacrificial agents. Moreover, the catalyst demonstrates practical applicability under natural sunlight with an NH₃ yield of 220.6 µmol h^-1 g^-1, suggesting its potential as a solar-driven nitrogen fertilizer. This is further validated by its successful application in cultivating Scenedesmus obliquus, exhibiting efficient nitrogen resource utilization. This work not only advances bioinspired nitrogenase-mimicking catalyst design but also establishes a sustainable solar-to-chemical energy conversion pathway.