Elucidating the Microenvironment Structure-Activity Relationship of Cu Single-Site Catalysts via Unsaturated N,O-Coordination for Singlet Oxygen Production

Understanding the microenvironment structure-activity relationship of singlet-atom catalysts (SACs) is imperative for the development of high-performance photocatalytic devices. However, the challenge remains to finely regulate the coordination microenvironment of SACs. Herein, single-atom N_x─Cu─O_4-x (x = 1–4) photocatalysts with different coordination environments are successfully prepared based on pre-design reticular supramolecular covalent organic frameworks (COFs) for direct photocatalytic ¹O₂ production from O₂. The results show that the high activity of Cu SACs is closely related to the N,O-coordination microenvironment, which is primarily ascribed to the different electrophilicity of the N, O atom. The electron configuration of N_3-Cu-O₁ endows photocatalyst enhanced charge transfer capability and the nearest D-band center to the Fermi level. The “end-on” type adsorption configuration of O₂ at the N₃─Cu─O₁ active site can promote the breaking of Cu─O bonds rather than O─O bonds. As a result, the N₃-Cu-O₁@COF photocatalyst exhibits the most optimal formation and desorption energies for intermediates •OOH, which provides an advantageous reaction pathway with fewer steps and a lower barrier for ¹O₂ production. This work highlights the structure-activity relationship of SACs for long-term applications.