Regulating the Built-In Electric field in Covalent Organic Frameworks for Enhanced CO2 Photoreduction: Asymmetry Linkage Structures

Covalent organic frameworks (COFs) are an emerging kind of photocatalysts which convert CO2 to value-added fuels. However, COFs usually exhibit lower catalytic efficiency without using metal, sacrificial reagent, or photosensitizer due to their easy electron-hole recombination. Herein, a series of imine-linked COFs with different asymmetric linkage structures have been synthesized to enhance the separation efficiency of photoexcited electron-hole pairs in the COFs by tuning the intramolecular built-in electric-field strength. The OH-COF exhibits a high CO production rate of 616 mu mol g(-1) in the 4 h reaction with similar to 100% selectivity, which surpasses most of the metal-free COF photocatalysts reported in the literature. This reveals that the higher polarity of OH-COF with an asymmetric linkage structure leads to a stronger built-in electric-field strength and a faster charge-transfer rate and thus more efficient photocatalytic performance. This work would provide some insights into the built-in electric-field design of COFs for efficient CO2 photoreduction.