Spatial Confinement of Pd Nanoclusters in Pyrene-Based Covalent Organic Frameworks for Boosting Photocatalytic CO2 Reduction

Photocatalytic CO₂ reduction offers a promising strategy to mitigate the greenhouse effect, yet it remains a challenging process due to the high energy barrier associated with the high stability of CO₂. In this study, we synthesized Py-bTDC, a pyrene-based covalent organic framework (COF) enriched with nitrogen and sulfur atoms, and anchored palladium nanoclusters (Pd NCs) onto its structure to enhance CO₂ reduction efficiency. The confined Pd NCs amplify the built-in electric field (IEF), enabling efficient photogenerated carrier migration and suppressing electron-hole recombination. Simultaneously, Pd NCs serve as catalytic active sites, optimizing CO₂ adsorption and activation. Density functional theory (DFT) calculations reveal that Pd reduces the energy barrier for forming the critical intermediate (*COOH), thereby accelerating CO production. Under visible-light irradiation in a gas-solid system using water as a proton donor, the Pd₃/Py-bTDC composite achieved a CO evolution rate of 17.75 µmol·h⁻¹·g⁻¹ with 86.0% selectivity. This study advances the design of COF-based photocatalysts by synergistically modulating IEF and the engineering active sites for efficient CO₂ reduction.