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

Abstract

Carbon monoxide reduction reaction (CORR) to yield value-added methanol entails the delicate design of catalysts due to the large overpotential of this reaction. 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 vs. RHE, surpassing that of CityU-34 (2.1%) with only Co atoms. The enhanced methanol production originates from the optimization of electronic structure with improved *CO adsorption, which is substantiated by the spectroscopic shift in UV and X-ray photoelectron spectroscopy and a stronger *CO signal in 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 in CityU-35 not only improves the adsorption towards *CO intermediates but also supplies a fast generation of protons for the hydrogenation of *CO towards CH3OH. The optimized electronic structures with synergistic effects between Co and Ni sites after cascaded metalation reduce the energy barriers and improve the overall electroactivity.