Cu-based electrocatalysts with favorable facets and Cu+ can boost CO2 reduction to valuable multi-carbon products. However, the inevitable Cu+ reduction and phase evolution usually result in poor performance. Herein, we fabricate CuI nanodots with favorable (220) facets and stable Cu+ state, accomplished by operando reconstruction of Cu(OH)2 under CO2- and I--contained electrolyte for enhanced CO2-to-C2H4 conversion. In-situ Raman spectroscopy and thermodynamic potential analysis reveal the preferred formation of CuI which is stabilized by I-; vacuum gas electroresponse experiments and density functional theory (DFT) calculations demonstrate that CO2-related species induce the exposure of (220) of CuI. The resulting electrocatalysts exhibit a high C2H4 Faradaic efficiency of 72.4% at a large current density of 800 mA cm-2 and robust stability for 12 h in a flow cell. Combined in-situ ATR-SEIRS spectroscopic characterizations and DFT calculations indicate the (220) facets and stable Cu+ in CuI synergistically facilitate CO2/*CO adsorption and *CO dimerization.
