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

Abstract

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 FE_CO 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.