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

Abstract Photocatalytic nitrogen reduction to ammonia (NH ₃ ) 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 (Fe ₄ S ₄ and Fe ₂ S ₂ ) is rationally designed and synthesized. Guided by the hard‐soft acid‐base (HSAB) theory, the Fe ² ⁺/Fe ³ ⁺ 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 Fe ₄ S ₄ exhibits strong N ₂ adsorption energy and enhances charge carrier mobility, while Fe ₂ S ₂ , 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 NH ₃ 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 NH ₃ 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.