Cu-Based Diatomic Catalysts for Electrochemical Reduction of CO₂ to Ethylene: A First-Principles Study

Appropriate CO adsorption and facile C-C coupling are the core factors in the electro-reduction of CO₂ into multicarbon (C₂₊) products. Diatomic catalysts possess the capability to precisely modulate the adsorption intensity of intermediates at two distinct active sites, which in turn effectively decreases the overpotential required for C-C coupling reactions. The first-principles study investigates the mechanism and activity of the CO₂RR on M/Cu-NG (M = Zn, Pd, Sn, Ag, or Au). The formation energy and dynamics analysis confirm that all M/Cu-NGs have good thermodynamic stability. Still, the dissolution potential indicates that the electrochemical stability of Zn is unstable, and the Zn atom is easily dissolved. It is found that only Sn/Cu-NG and Pd/Cu-NG have CO₂RR selectivity and tend to be completed through the *COOH intermediate through selective analysis of the HER and CO₂RR. Subsequently, a detailed study is conducted on the adsorption and charge transfer of *CO₂, *CO, and *C₂H₄ on these two catalysts. Interestingly, it is suggested that C-C coupling on Sn/Cu-NG may occur between *CO and *CHO rather than between *CO and *CO by analyzing COHP. Finally, we calculated the entire pathway and found that CO₂ is reduced to ethylene mainly through the *COHCHOH route on Sn/Cu-NG, which has a high ΔG value of PDS (*CO-*CO → *CO-*CHO) of 0.96 eV and a high coupling energy barrier (1.23 eV), resulting in a U_L of -0.96 V. On Pd/Cu-NG, ethylene is mainly generated through the *HCCO route, and the PDS is *CO-*CO → *COCO. This step has a smaller ΔG value of 0.71 eV and a coupling energy barrier of 0.61 eV, resulting in a U_L of -0.71 V for the entire reaction.