Axial F-Bi-O_v Electron Pump Drives Continuous Reconfiguration of Bi Sites for Efficient Photocatalytic N₂ Reduction

The electronic structure precision of single-atom catalysts (SACs) represents a decisive factor limiting advancements in photocatalytic nitrogen reduction (NRR) efficiency. This study addresses this issue by simultaneously introducing an axial fluoride ligand (F^-) and engineering surface oxygen vacancies (O_v) around atomically dispersed Bi centers supported on W₁₈O₄₉ (denoted as FBWO). The axial fluoride ligand withdraws electron density away from the Bi site, increasing surface hydrophobicity and forming a surface dipole. This dipole lowers the conduction band while promoting side-on N₂ chemisorption. Meanwhile, photo-induced O_v accumulate electrons around Bi site, forming a continuous F-Bi-O_v "electron pump" that reduces the activation energy for the first proton-electron transfer from 1.69 eV (on pristine W₁₈O₄₉ with single Bi sites, BWO) to 0.87 eV (on FBWO). These synergistic electronic and energetic modifications enable the material to achieve a visible-light NH₃ production rate of 354.2 µmol g^-1·h^-1-8.4 times that of pristine W₁₈O₄₉ and twice that of BWO-surpassing all recently reported Bi- and W-based photocatalysts for N₂ reduction. This work provides a unified design strategy that integrates ligand-field engineering with defect chemistry, facilitating the targeted development of SACs into high-performance photocatalysts for sustainable ammonia production.″.