Ternary Metalation in a Copper‐Covalent Organic Framework for Tandem Photocatalytic CO ₂ Reduction with High Selectivity

Abstract Developing multifunctional photocatalysts with efficient synergistic effects for selective photocatalytic CO 2 reduction is sought‐after yet challenging. Herein, a tandem photocatalytic strategy has been developed through sequential post‐synthetic metalation (SPSM) of variable Ru/Co‐sites into a trinuclear Cu‐based COF, Cu 3 ‐BPY‐COF, to construct a series of tri‐metallized covalent‐organic frameworks (COFs), Cu 3 ‐BPY‐COF(Ru/Co)‐X (X = 1, 2, or 3, corresponding to the Ru:Co molar ratios of 1/39.6, 1/19.6, or 1/12.7, respectively), for photocatalytic CO 2 methanation in high selectivity. The introduction of a small fraction of Ru‐sites confers the framework with enhanced visible‐light response, while the Co‐sites immobilized in the bipyridine units significantly boost the generation of CO to enrich its concentration around the active trinuclear Cu‐sites, which enables dramatically improved photocatalytic CO 2 reduction activity toward CH 4 . Significantly, the optimized Cu 3 ‐BPY‐COF(Ru/Co)‐2 showcases exceptional photocatalytic activity with a CH 4 evolution rate of 31.5 µmol g −1 h −1 and selectivity of 95%, 15.0 times higher than that of Cu 3 ‐BPY‐COF(Ru) merely introducing Ru‐photosensitizer. The underlying photocatalytic mechanism has been studied to unveil how the ternary Ru/Co/Cu‐sites collaborate to result in highly efficient and selective CO 2 ‐to‐CH 4 reduction, shedding light on the design of highly selective CO 2 methanation photocatalysts by leveraging the synergistic effect of multiple active centers within heterometallic covalent‐organic frameworks (HM‐COFs).