Dual Defects‐Induced Iron Single Atoms Immobilized in Metal–Organic Framework‐Derived Hollow BiOBr Microtubes for Low‐Barrier Photocatalytic Nitrogen Reduction

Abstract

The rational design of single-atom catalysts with precise coordination environment and high separation efficiency of photogenerated carriers is critical yet challenging to achieve efficient photocatalytic nitrogen reduction. Herein, we design and construct a defective photocatalyst featuring Fe single atoms immobilized in hollow BiOBr microtube using a plasma-assisted synthesis strategy, where the Bi-based metal-organic framework is used as sacrificial template. The dual vacancies of oxygen (V_O) and bromine (V_Br) are created in the BiOBr microtube and induce the formation of coordinatively unsaturated FeO₅ configuration, where four oxygen atoms are from [Bi₂O₂]²⁺ units and one oxygen atom is located in the V_Br. Specially, the hollow catalyst with dual defects and FeO₅ moiety exhibits 1.4 and 2.2 times higher ammonia production activity than another two V_Br-featuring catalysts with coordinatively saturated FeO₆ configuration and unsaturated FeO₄ configuration, respectively. As revealed by experimental and theoretical calculation results, the optimized catalyst with the FeO₅ configuration reduces the energy barrier of electron transfer from Fe 3d orbitals to antibonding orbitals of N₂ molecules, which favors the formation of a key *NNH intermediate in the N₂ fixation reaction and the resultant efficient ammonia production.