Origin of copper as a unique catalyst for C-C coupling in electrocatalytic CO₂ reduction

High yields of C₂ products through electrocatalytic CO₂ reduction (eCO₂R) can only be obtained using Cu-based catalysts. Here, we adopt the generalized frontier molecular orbital (MO) theory based on first-principles calculations to identify the origin of this unique property of Cu. We use the grand canonical ensemble (or fixed potential) approach to ensure that the calculated Fermi level, which serves as the frontier orbital of the metal catalyst, accurately represents the applied electrode potentials. We determine that the key intermediate OCCO assumes a U-shape configuration with the two C atoms bonded to the Cu substrate. We identify the frontier MOs that are involved in the C-C coupling. The good alignment of the Fermi level of Cu with these frontier MOs is perceived to account for the excellent catalytic performance of Cu for C-C coupling. It is expected that these new insights could provide useful guidance in tuning Cu-based catalysts as well as designing non-Cu catalysts toward high-efficiency eCO₂R.