Highly Efficient Electroconversion of CO₂ into CH₄ by a Metal–Organic Framework with Trigonal Pyramidal Cu(I)N₃ Active Sites

Abstract

High-efficiency electrocatalysts for CO2 reduction reaction are extremely desirable to produce valuable hydrocarbon productions, as well as addressing the current environmental challenges. In this work, we introduce a Cu-based metal–organic framework as a catalyst for the efficient and selective reduction of CO2 to CH4 in neutral aqueous electrolytes. Detailed examination of [Cu4ZnCl4(btdd)3] (Cu4-MFU-4l, H2btdd = bis(1H-1,2,3-triazolo-[4,5-b],[4′,5′-i])dibenzo-[1,4]-dioxin) revealed the highest activity for yielding methane with a Faradaic efficiency of 92%/88% and a partial current density of 9.8/18.3 mA cm–2 at a potential of −1.2/–1.3 V (vs RHE). In situ X-ray absorption and infrared spectroscopy spectra, as well as density functional theory calculations, revealed that the in situ generated trigonal pyramidal Cu(I)N3 acts as the electrochemical active site and that the strong coordination ability of the Cu(I)N3 site and the synergistic effect of adjacent aromatic hydrogen atoms, via hydrogen-bonding interactions, play an important role in stabilizing the key intermediates of carbon dioxide reduction and inhibiting the hydrogen evolution reaction, thus showing a high performance of electroreduction of CO2 to CH4.