Selective electroreduction of carbon dioxide to ethylene over stable iodide-induced asymmetric copper sites within a metal-organic polyhedron

We prepared a Cu-based metal-organic polyhedron, Cu-TCBB, and used it for CO 2 electroreduction. Cu-TCBB exhibits a high Faradaic efficiency towards C 2 H 4 of 73.1% at −1.1 V vs. RHE and excellent stability in 0.1 mol L −1 CsI aqueous solution. The one-way access of I − to the host has been shown to result in the formation of {Cu(II)·Cu(I)}, which is identified as the true active site for CO 2 electroreduction. Porous Cu-based metal-organic compounds have attracted increasing attention for CO 2 electroreduction due to their well-defined porous structures and abundant metal sites. However, the classical {Cu 2 }-paddlewheel moieties within these materials often show poor electrochemical stability, leading to structural degradation during CO 2 electroreduction. Here, we report a strategy to generate stable {Cu(II)·Cu(I)} active sites by iodide species in a Cu-based metal-organic polyhedron, Cu-TCBB (TCBB=1,3,5-tris(4′-carboxybiphenyl-2-yl)benzene), to not only promote C 2 H 4 production but also clarify the real active sites of {Cu 2 }-paddlewheel-based materials during CO 2 electroreduction. Cu-TCBB exhibits a high Faradaic efficiency (FE) of 73.1% towards C 2 H 4 at −1.1 V vs. reversible hydrogen electrode (RHE) in 0.1 mol L −1 CsI aqueous solution, outperforming all porous metal-organic compounds to date. The presence of iodide-induced {Cu(II)·Cu(I)} sites was verified through in situ synchrotron X-ray diffraction and absorption spectroscopy, electron paramagnetic resonance spectroscopy, coupled with modelling, shedding light on the mechanism of CO 2 electroreduction over unique {Cu(II)·Cu(I)} sites.