Ternary Metalation in a Copper‐Covalent Organic Framework for Tandem Photocatalytic CO2 Reduction with High Selectivity

Developing multifunctional photocatalysts with efficient synergistic effects for selective photocatalytic CO2 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, Cu3‐BPY‐COF, to construct a series of tri‐metallized covalent‐organic frameworks (COFs), Cu3‐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 CO2 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 CO2 reduction activity toward CH4. Significantly, the optimized Cu3‐BPY‐COF(Ru/Co)‐2 showcases exceptional photocatalytic activity with CH4 evolution rate of 31.5 μmol g‐1 h‐1 and selectivity of 95%, 15 times higher than that of Cu3‐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 CO2‐to‐CH4 reduction, shedding light on the design of highly selective CO2 methanation photocatalyst by leveraging the synergistic effect of multiple active‐centers within heterometallic covalent‐organic frameworks (HM‐COFs).