Site‐Specific for CO 2 Photoreduction with Single‐Atom Ni on Strained TiO 2−x Derived from Bimetallic Metal–Organic Frameworks

The photocatalytic reduction of CO₂ in water to produce fuels and chemicals is promising while challenging. However, many photocatalysts for accomplishing such challenging task usually suffer from unspecific catalytic active sites and the inefficient charge carrier's separation. Here, a site-specific single-atom Ni/TiO_2-x catalyst is reported by in situ topological transformation of Ni-Ti-EG bimetallic metal-organic frameworks. The loading of nickel nanoparticles or individual atoms, which act as specific active sites, can be precisely regulated by chelating agents through the partial removal of nickel and adjacent oxygen atoms. Furthermore, the degree of lattice strain in Ni/TiO_2-x catalysts, which improves the separation efficiency of charge carriers, can be modulated by fine-tuning the transformation process. By leveraging the anchored nickel atoms and the strained TiO₂, the optimized Ni_SA0.27/TiO_2-x shows a CO generation rate of 86.3 µmol g^-1 h^-1 (288 times higher than that of Ni_NPs/TiO_2-x) and CO selectivity of up to 92.5% for CO₂ reduction in a pure-water system. This work underscores the importance of tailoring lattice strain and creating specific single-atom active sites to facilitate the efficient and selective reduction of CO₂.