Efficient Syngas Photoproduction Enabled by Electronic Engineering of Co-Immobilized Imine COFs

Heterogeneous photocatalytic CO₂ reduction provides a promising route for syngas production. However, high reaction energy barriers and inefficient charge separation and transfer hinder the surface CO₂ reduction. Herein, on a covalent organic framework (COF) based catalyst, through the enhanced photoelectron transfer efficiency by introduction of N atoms, also the increased electron density of the Co (II) site with two negative one-valent bidentate ligands, we achieved both ultrahigh syngas production rate and high H₂/CO molar ratio. The best catalyst in this work: Triazine-COF-Co-SA enabled a record-high syngas production rate with high H₂/CO molar ratio (≥2) of 698.7 mmol g^-1 h^-1. Femtosecond transient absorption spectroscopy (fs-TAS), in situ infrared spectroscopy (In situ IR) and theoretical calculation indicated that N introduction to the framework and active site electron density increasing were effective for the previous challenges. On Triazine-COF-Co-SA, the energy barrier was lowered from 1.90 to 0.54 eV, also fs-TAS showed an obvious τ₄ = 1.5 ns which represented a higher charge transfer efficiency. This study shows great potential for catalyst modification on COF-based catalysts to enhance CO₂ photoreduction capability.