Co-doped Bi₂₄O₃₁Br₁₀ with photoswitchable Br, O binary vacancies synergistically provide dynamic active sites for N₂...

Ultra-thin two-dimensional bismuth oxyhalide with rich surface vacancies is an ideal material for photocatalytic nitrogen reduction reaction (NRR) of ammonia synthesis. However, the repair of these vacancies during the reaction invalidates its unique local microenvironmental advantage as an active site. Herein, ultra-thin Co-doped Bi₂₄O₃₁Br₁₀ (Co-BOB) nanosheets with photo-switchable Br, O binary vacancies were synthesized by a hydrothermal method. The surface Br and O vacancies were generated under light and filled again with migrated Br^- and O in solution at air atmosphere under dark. The Br vacancies serve as a medium for electron accumulation and transfer facilitating interlayer charge transfer. The O vacancies generate charge delocalization and lead to the local electron-deficient site, which promotes the adsorption and activation of N₂. In addition, density functional theory calculation show that N₂ reduction follows an alternating association pathway producing ammonia on the surface of Co-BOB. The photogenerated vacancies reduce the energy barrier of the first proton-coupled electron transfer process acting as a rate-determining step. The ammonia production rate of 5 % Co-BOB is 120.3 µmol g^-1 h^-1, which is 6.23 times higher than initial BOB. Meanwhile, the unique photoswitchable protection mechanism ensures the excellent recyclability of Co-BOB. Experiments and calculations reveal the role of formation of photoswitchable Br, O binary vacancies on Co-BOB nanosheets for efficient and stable NRR performance. This work provides a new strategy for promoting sustainable NRR by combining photoswitchable facilitated reaction with the active site regeneration.