Engineering Single Cu Atoms Anchored via N‐Heterocyclic Carbene in COF Mesopores for Modulating Electron Kinetics of CO₂ Photoconversion.

Charge transfer and carbon dioxide (CO2) adsorption/activation are critical factors for the electron kinetics during CO2 photoconversion. Herein, high‐loading and robust single Cu atoms (7.8 wt.%) are anchored via N‐heterocyclic carbene ligands derived from imidazolium ionic liquid motifs, precisely bonding to the acceptors of mesoporous donor‐acceptor pyridine‐covalent organic framework (pCOF) nanosheets. By engineering the valance and coordination structure, atomic Cu(I)‐CO2 sites, superior to Cu(II)‐CN2OCl ones, enable a 22‐fold increase of CO2 conversion rate compared to pCOF in pure water, ≈100% selectivity toward CO, and an apparent quantum yield of 1.7% (420 nm). The photoactivity outperforms analogous COF‐based photocatalysts under similar conditions. Experimental results prove single Cu(I) atoms possess more improved electron capture and CO2 adsorption/activation capacities than single Cu(II) ones. Combining fs‐ and µs‐transient absorption spectroscopy, the electron kinetics mechanism is investigated on the single‐atom pCOF photocatalyst model. The fs‐transient absorption spectra confirm single Cu(I) atoms can rapidly and precisely extract electrons from the electron‐rich region of pCOF along N‐heterocyclic carbene, exhibiting an electron transfer rate of 3 × 109 s−1. Using in situ µs‐transient absorption spectroscopy, the electron transfer efficiency is quantified to reach 60.4% under photocatalytic reaction conditions. This work provides a rational design strategy for advanced single‐atom photocatalysts. [ABSTRACT FROM AUTHOR]