Cascaded Metalation of Two-Dimensional Covalent Organic Frameworks for Boosting Electrochemical CO Reduction.

The electrochemical CO reduction reaction (CORR) to high-value methanol requires the delicate design of catalysts due to the large overpotential. Especially, achieving precise modification of electrocatalysts while preserving the periodic alignment of active sites to optimize performance remains a significant challenge. Here, we report the cascaded metalation of phthalocyanine-based COFs for selective reduction of CO to methanol. After implanting the secondary metal (Ni), CityU-35 achieves a Faradaic efficiency (FE) of 48.4% at -0.85 V versus RHE, significantly surpassing that of CityU-34 (2.1%) with only Co atoms. Enhanced methanol production originates from the optimization of electronic structure with improved *CO adsorption, as substantiated by the in situ attenuated total reflectance surface-enhanced infrared absorption spectroscopy (ATR-SEIRAS). Theoretical calculations have demonstrated that the cascaded metalation with the introduction of secondary Ni sites not only strengthens *CO adsorption but also accelerates proton generation for the hydrogenation of *CO toward CH3OH. The cascaded metalation with synergistic effects between Co and Ni sites reduces the energy barriers and improves the overall electroactivity. Our results demonstrate cascaded metalation as an effective strategy to tailor the catalytic activities of 2D COFs, extending the functional design of reticular frameworks in electrocatalysis.