Regulating local charge distribution of single Ni sites in covalent organic frameworks for enhanced photocatalytic CO2 reduction.

A series of isostructural covalent organic frameworks (COFs) were developed for CO 2 photoreduction. The strong coordination conformation guides atomically dispersed metal sites to chelate in the predesigned imine-pyridine position on the ordered channel walls of COFs. The COFs exhibited substantially enhanced activity even using diluted CO 2 under sunlight owing to the single-Ni site engineering and electronic structures of COF configuration. [Display omitted] • A series of isostructural COFs bearing imine-pyridine moieties formed by pyridine units and their adjacent imine groups anchoring single-Ni sites. • Local charge distribution of single Ni sites can be regulated by tuning the electron character of chemical structural units. • The optimal Ni-TAPT-COF achieved a record-high CO production rate, even for natural-sunlight-driven low-concentration CO 2. • The synergetic effect of the COF configuration and single-Ni site can promote charge separation/transfer efficiency and CO 2 adsorption and activation. Covalent organic frameworks (COFs) engineered by single-atom sites have attracted significant attention for CO 2 photoreduction. However, precisely manipulating the chemical environment of active sites on the COFs is a grand challenge. Herein, we synthesized a series of isostructural COFs for photocatalytic CO 2 reduction, where the strong coordination conformation guides atomically dispersed metal sites to chelate spontaneously in the predesigned imine-pyridine position of COFs. Experimental and theoretical results revealed the crucial influence of the single-Ni site engineering and electronic structures of COF configuration on improving extended π-conjugation, exciton dissociation, charge separation efficiency, and charge carrier migration. Benefiting from the synergistic effect, the optimal Ni-TAPT-COF exhibited a record-high CO production rate of 25.5 mmol g-1h-1 and a selectivity of 98.8%, even natural-sunlight-driven diluted CO 2 (10%). This work paves the way for the rational design of high-performance COF-based photocatalysts at the molecular level, highlighting their practical potential for CO 2 photoreduction. [ABSTRACT FROM AUTHOR]