Highly efficient and selective photocatalytic CO2 reduction to CO via molecular engineering of covalent organic framework

Covalent organic frameworks (COFs) are garnering significant interest in photocatalytic CO₂ reduction. However, their limited efficiency in separating photogenerated carriers and the scarcity of catalytic sites lead to suboptimal photocatalytic performance. Here we develop a molecular engineering approach to design a pyrene-based COF (PyTa-H COF) confined cobalt single atoms photocatalyst (Co SACs) for CO₂ reduction. Pyrene moiety is introduced to enhance visible-light harvesting capability and improve charge separation in the COF. Subsequently, Co SACs enhance the photocatalytic activity by accelerating the migration of photo-induced carriers and reducing the reaction energy of the rate-determining step. Remarkably, PyTa-H@Co achieves a CO production rate of 18.36 mmol g⁻¹ h⁻¹ and a selectivity of 94% in 4 h under visible light irradiation, which is comparable to the reported best-performing COFs. Density functional theory calculations reveal that the Co SACs greatly stabilize *COOH and significantly reduce the energy of the decisive step, leading to outstanding photocatalytic performance. This work, through molecular engineering design, highlights the critical relationship between catalyst structure and function in enhancing photocatalytic efficiency.