Regulation of Coordinating Anions around Single Co(II) Sites in a Covalent Organic Framework for Boosting CO2 Photoreduction

While photocatalytic CO2 reduction has been intensively investigated, reports on the influence of anions coordinated to catalytic metal sites on CO2 photoreduction remain limited. Herein, different coordinated anions (F–, Cl–, OAc–, and NO3–) around single Co sites installed on bipyridine-based three-component covalent organic frameworks (COFs) were synthesized, affording TBD-COF-Co-X (X = F, Cl, OAc, and NO3), for photocatalytic CO2 reduction. Notably, the presence of these coordinated anions on the Co sites significantly influences the photocatalytic performance, where TBD-COF-Co-F exhibits superior activity to its counterparts. Combined experimental and theoretical results indicate that the enhanced activity in TBD-COF-Co-F is attributed to its efficient charge transfer, high CO2 adsorption capacity, and low energy barrier for CO2 activation. This study provides a new strategy for boosting COF photocatalysis through coordinated anion regulation around catalytic metal sites.