Selective C₂ Electroproduction via Back Bonding in Asymmetric Copper-Copper Motifs

CO₂ reduction reaction (CO₂RR) is considered a highly attractive approach to reduce carbon emissions and yet encounters challenges in further converting *C₁ intermediates to valuable two-carbon (C₂) products. Although copper-based catalysts exhibit satisfactory adsorption energy for *C₁ species, the symmetrical charge distribution at adjacent copper sites leads to a strong repulsive force between adsorbed *C₁. Herein, asymmetric copper-copper (Cu_F-Cu_N) motifs with distinct adsorption behaviors have been constructed on the F-Cu₃N substrate using the in situ isostructural substitution method. Compared to the high hybridization of Cu_N 3d and N 2p orbitals, implanted F not only reduces the hybridization strength but also endows the Cu_F with delocalized unpaired electrons. Accordingly, Cu_F, beyond forming an isolated 3d_z ²-2p_z σ bond between Cu and the key *C₁ intermediate (*CHO), offers additional 3d_xz-2p_z π back bonding to the *CHO. With dipole interactions in the asymmetric Cu_F-Cu_N motifs, the electrostatic repulsion between adjacent *CHO is diminished, efficiently promoting the C-C coupling in CO₂RR. Therefore, the Cu_F-Cu_N motifs achieve an exceptional C₂ selectivity of 81.5% with a partial current density of -325.9 mA cm^-2 and a C₂/C₁ selectivity ratio of 10.47. This nuanced manipulation of atomic interactions illuminates a path to potentially groundbreaking alterations in material characteristics.