Two-Dimensional Kagome Covalent Organic Frameworks with Single Atomic Co Sites for Superior Photocatalytic CO2 Reduction

Covalent organic frameworks (COFs) have attracted great attention as pivotal photocatalysts for efficient CO2 photoreduction into value-added fuels, which hold great promise for simultaneously mitigating global warming and the energy crisis. However, the synthesis of COFs with a high crystalline state and hierarchically porous structure to boost CO2 photoreduction is still an enormous challenge and rarely reported, probably because of the great dependence upon monomers and rigorous preparation conditions. Herein, a series of functional kagome (kg m) topologic 2D COFs with high crystallinity and porosity were synthesized based on the condensation of 4,4′,4″,4‴-(ethene-1,1,2,2-tetrayl)tetraaniline (ETTA) and 2,2′-bipyridyl-5,5′-dialdehyde (Bpy-CHO) building units combined with a postmodification strategy, named ETTA-Bpy-COF-M (M = H, Fe, Co, Ni, or Cu). Stimulated by the unique kg m topologized framework with well-ordered hierarchical micropores and mesopores, abundant exposed atomic Co sites, and remarkable photoelectrical performance, ETTA-Bpy-COF-Co is used as a photocatalyst for catalyzing the CO2-to-CO photoconversion and exhibits a high CO yield rate (9398.14 μmol g–1 h–1), a large CO selectivity (92.73%), and good durability. Experimental and theoretical analyses demonstrated that the superior performance for CO2 photoreduction catalyzed by ETTA-Bpy-COF-Co was attributed to the desirable cooperative contribution of kg m topological structure with hexagonal and triangular pores as well as atomic Co active sites, which can promote the photoexcited charge carrier kinetics, enhance the CO2 adsorption and activation, as well as reduce the energy barriers of *COOH generation and CO desorption. This work opens a new way to enhance COF photosynthesis for CO2 reduction and offers precious insights into related studies in the future.