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Photocatalytic oxygen reduction reactions and water oxidation reactions are extremely promising green approaches for massive H2O2 production. Nonetheless, constructing effective photocatalysts for H2O2 generation is critical and still challenging. Since the network topology has significant impacts on the electronic properties of two dimensional (2D) polymers, herein, for the first time, we regulated the H2O2 photosynthetic activity of 2D covalent organic frameworks (COFs) by topology. Through designing the linking sites of the monomers, we synthesized a pair of novel COFs with similar chemical components on the backbones but distinct topologies. Without sacrificial agents, TBD‐COF with cpt topology exhibited superior H2O2 photoproduction performance (6085 and 5448 μmol g−1 h−1 in O2 and air) than TBC‐COF with hcb topology through the O2‐O2⋅−‐H2O2, O2‐O2⋅−‐O21‐H2O2, and H2O‐H2O2 three paths. Further experimental and theoretical investigations confirmed that during the H2O2 photosynthetic process, the charge carrier separation efficiency, O2⋅− generation and conversion, and the energy barrier of the rate determination steps in the three channels, related to the formation of *OOH, *O21, and *OH, can be well tuned by the topology of COFs. The current study enlightens the fabrication of high‐performance photocatalysts for H2O2 production by topological structure modulation. [ABSTRACT FROM AUTHOR]

Covalent organic frameworks (COFs) with bioinspired N,S-sites were constructed. Single Co atoms were coordinated with N,S-sites to create Co-THD-COF, which photocatalyzed CO 2 conversion to CO with 95.1 % selectivity in water and natural seawater. The synergistic interaction between THD-COF and the single atomic Co center enhanced CO 2 adsorption, activation, and reduced reaction energy barriers for *COOH intermediates, resulting in good performance. [Display omitted] • Learning from natural carbon monoxide dehydrogenase, we delicately designed a THD-COF with bioinspired N,S-coordination sites and constructed Co-THD-COF by anchoring single Co atoms on the N,S-sites. • Co-THD-COF can photocatalyze CO 2 conversion to CO with 95.1 % selectivity in water and natural seawater with reusability. • Under visible light, Co-THD-COF displayed dramatically enhanced photocatalytic CO 2 RR activity, exhibiting the CO generating rate of 9357 μmol g−1h−1. • The synergistic interaction between THD-COF and the single atomic Co center enhanced CO 2 adsorption, activation, and reduced reaction energy barriers for *COOH intermediates, resulting in good performance. Photocatalytic CO 2 reduction reaction (CO 2 RR) has promising potential to address global energy and environmental challenges but is severely limited by sluggish kinetics and poor selectivity, where the chemical microenvironments and electronic structures of the catalytic center play pivotal roles. Herein, inspired by carbon monoxide dehydrogenase, which can accelerate CO 2 to CO reduction, we delicately design a covalent organic framework (THD-COF) with bioinspired N,S-coordination sites from thiophene and imine modules on the skeleton and construct Co-THD-COF by anchoring single Co atoms on the N,S-sites. Under visible light, employing binary mixed sacrificial agents, with the help of photosensitizer [Ru(bpy) 3 ]Cl 2 ·6H 2 O, Co-THD-COF displays dramatically enhanced photocatalytic CO 2 RR activity, exhibiting an astounding CO generating rate of 9357 μmol g−1h−1 with the selectivity of 95.1 %. Additionally, Co-THD-COF can photocatalyze CO 2 conversion smoothly in real seawater without loss of CO selectivity. Experimental and computational analysis further manifest that the single Co atom is the catalytic active center. Co-THD-COF significantly promotes CO 2 adsorption and activation, charge separation dynamics, and is also beneficial to the formation of the crucial *COOH intermediates. The current study offers deep insights into the effective conversion of CO 2 and enlightens the design of novel bioinspired coordination sites for single-atom photocatalysts. [ABSTRACT FROM AUTHOR]