Covalent Organic Framework Stabilized Single CoN₄Cl₂ Site Boosts Photocatalytic CO₂ Reduction into Tunable Syngas

Solar carbon dioxide (CO₂) reduction provides an attractive alternative to producing sustainable chemicals and fuel. However, the construction of a highly active photocatalyst was challenging because of the rapid charge recombination and sluggish surface CO₂ reduction. Herein, a unique Co-N₄Cl₂ single site was fabricated by loading Co species into the 2,2'-bipyridine and triazine-containing covalent organic framework (COF) for CO₂ conversion into syngas under visible light irradiation. The resulting champion catalyst TPy-COF-Co enabled a record-high CO production rate of 426 mmol g^-1 h^-1, associated with the unprecedented turnover number (TON) and turnover frequency (TOF) of 2095 and 1607 h^-1, respectively. The catalyst also exhibited favorable recycling performance and widely adjustable syngas production (CO/H₂ ratio: 1.8 : 1-1 : 16). A systematical investigation including operando synchrotron X-ray absorption fine structure (XAFS) spectroscopy, in situ attenuated total reflection surface-enhanced infrared absorption spectroscopy (ATR-SEIRAS), and theoretical calculation indicated that the triazine-based COF framework promoted the charge transfer towards the single Co-N₄Cl₂ sites that greatly promoted the CO₂ activation by lowering the energy barrier of *COOH generation, facilitating the CO₂ transformation. This work highlights the great potential of the molecular regulation of COF-derived single-atom catalysts to boost CO₂ photoreduction efficiency.