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

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.