Highly Selective CO₂ Electroreduction to C₂H₄ Using a Metal–Organic Framework with Dual Active Sites

Abstract

Conversion from CO₂ to C₂H₄ is important for the development of energy and the environment, but the high energy barrier of hydrogenation of the *CO intermediate and C-C coupling step tend to result in C₁ compounds as the main product and thus restrict the generation of C₂H₄. Here, we report a metal-organic framework (denoted as PcCu-Cu-O), composed of 2,3,9,10,16,17,23,24-octahydroxyphthalo-cyaninato)copper(II) (PcCu-(OH)₈) ligands and the square-planar CuO₄ nodes, as the electrocatalyst for CO₂ to C₂H₄. Compared with the discrete molecular copper-phthalocyanine (Faradaic efficiency (FE) of C₂H₄ = 25%), PcCu-Cu-O exhibits much higher performance for electrocatalytic reduction of CO₂ to C₂H₄ with a FE of 50(1)% and a current density of 7.3 mA cm^-2 at the potential of -1.2 V vs RHE in 0.1 M KHCO₃ solution, representing the best performance reported to date. In-situ infrared spectroscopy and control experiments suggested that the enhanced electrochemical performance may be ascribed to the synergistic effect between the CuPc unit and the CuO₄ unit, namely the CO on the CO-producing site (CuO₄ site) can efficiently migrate and dimerize with the *CO intermediate adsorbed on the C₂H₄-producing site (CuPc), giving a lower C-C dimerization energy barrier.