Axial F–Bi–O _v Electron Pump Drives Continuous Reconfiguration of Bi Sites for Efficient Photocatalytic N ₂ Reduction

ABSTRACT 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 W ₁₈ O ₄₉ (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 N ₂ 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 W ₁₈ O ₄₉ 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 NH ₃ production rate of 354.2 µ mol g ⁻¹ ·h ⁻¹ –8.4 times that of pristine W ₁₈ O ₄₉ and twice that of BWO—surpassing all recently reported Bi‐ and W‐based photocatalysts for N ₂ 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.″