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

Porous Cu-based metal-organic compounds have attracted increasing attention for CO2 electroreduction due to their well-defined porous structures and abundant metal sites. However, the classical {Cu2}-paddlewheel moieties within these materials often show poor electrochemical stability, leading to structural degradation during CO2 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 C2H4 production but also clarify the real active sites of {Cu2}-paddlewheel-based materials during CO2 electroreduction. Cu-TCBB exhibits a high Faradaic efficiency (FE) of 73.1% towards C2H4 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 CO2 electroreduction over unique {Cu(II)·Cu(I)} sites.