Robust imidazole-linked Ni-phthalocyanine-based covalent-organic framework for CO₂ electroreduction in the full pH range

The electroreduction of CO2 to value-added chemicals is a promising approach to utilize CO2 and mitigate greenhouse gas emission. Covalent organic frameworks (COFs) with abundant accessible active sites, tunable pore size, and large CO2 adsorption capacity are considered promising electrocatalysts for CO2 conversion. However, most COFs linked by reversible covalent bonds exhibit poor stability, which limits their application for CO2 electroreduction reactions in acidic or alkaline electrolytes. Herein, a Ni-phthalocyanine-based COF linked by stable imidazole building blocks, named NiPc-Im-COF, was synthesized through the condensation reaction of 2,3,9,10,16,17,23,24-octa-aminophthalocyaninato Ni(II) and 4,4 '-biphenyl dialdehyde. The obtained NiPc-Im-COF exhibits high chemical stability after soaking in concentrated HCl and KOH. When applied for the electroreduction of CO2, the NiPc-Im-COF exhibits high CO selectivity (>90%) in electrolytes with different pH values. Specifically, the NiPc-Im-COF shows a high CO partial current density of 267 mA cm(-2) with a CO selectivity of 90% at -0.8 V vs. the reversible hydrogen electrode (RHE) in 5 M KOH solution, and meanwhile, over 90% of FECO and 6 hours of stability at -1.3 V in 0.5 M K2SO4 (pH = 1). The XRD patterns prove that the structure of the NiPc-Im-COF is not destroyed after CO2 electroreduction at different pH values. This work presents a strategy to improve the stability of COFs via irreversible covalent linkage and offers an efficient CO2RR in the full pH range, which paves a new pathway for the industrial application of COFs in CO2 electroreduction.