Gram-scale synthesis of high-loading single-atom Ni catalysts anchored on vinylene-linked covalent organic frameworks for efficient photocatalytic carbon dioxide reduction

Single-atom catalysts (SACs) with atomically dispersed active centers exhibit high catalytic efficiency. However, simultaneously achieving high metal loading and scalable synthesis of SACs remains a major challenge, greatly limiting their practical deployment. Herein, we design a chemically robust covalent organic framework (COF) featuring an ordered porous structure and the precisely engineered coordination environment to immobilize single metal atoms at a relatively high loading. The vinylene-linked COF (PZBpy-COF) was synthesized through a solvent-free melt polymerization of tetramethylpyrazine and bipyridine monomers, followed by coordination of nickel (Ni) ions to afford Ni-PZBpy-COF with a high metal loading of 6.4 wt%. Aberration-corrected high-angle annular dark-field scanning transmission electron microscopy imaging confirms the uniform atomic dispersion of Ni sites throughout the COF matrix. Ni-PZBpy-COF shows an outstanding carbon dioxide (CO₂) photoreduction activity under visible-light irradiation, affording a carbon monoxide (CO) evolution rate of 5270 μmol g^-1 h^-1 with 90% selectivity for CO over hydrogen (H₂) evolution. Notably, the solvent-free strategy enables gram-scale preparation of PZBpy-COF while preserving crystallinity, porosity, uniform single-atom dispersion, and photocatalytic performance, addressing the scalability gap of COF-based photocatalysts predominantly synthesized at the milligram scale. The integration of COF structural tunability and synthetic scalability with the atomic precision of single-atom catalysts offers a viable route toward practical applications.