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

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 (VO) and bromine (VBr) 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 VBr. Specially, the hollow catalyst with dual defects and FeO5 moiety exhibits 1.4 and 2.2 times higher ammonia production activity than another two VBr-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.