Heteroatom-Engineered Triatomic Cu Cluster on G-C3N4 for Selective CO2-to-Ethylene Electrocatalysis.

Electrochemical reduction of CO2 into multi-carbon products offers a sustainable route to carbon recycling, yet achieving selective C─C coupling remains challenging. Here, we investigate the performance of heteroatom-doped Cu3 clusters supported on g-C3N4 for CO2-to-C2H4 conversion. Through DFT calculations and transition-state analysis, we demonstrate that doping with P and Se stabilizes the Cu3 clusters, enhances *CO adsorption, and lowers the energy barrier for the rate-determining *CO + *CHO → *COCHO C─C coupling step to 0.84 and 0.92 eV, respectively. Thermodynamic analysis reveals a preference for ethylene formation over ethanol, with overpotentials as low as 0.33 and 0.10 V for P- and Se-doped systems. Electronic structure analysis shows that first-shell substitution with P or Se creates charge-asymmetric sites, strengthens *CO and *CHO binding, and shifts antibonding Cu─CO states to higher energies, thereby promoting efficient C─C coupling. Electrochemically, the Se-modified catalyst delivers a remarkable ethylene Faradaic efficiency of ∼54% at 250 mA cm-2, and maintains stable performance for 30 h under flow-cell conditions. This study establishes a synergistic theory-experiment framework for optimizing CO2RR catalysts, emphasizing the critical role of precise cluster engineering and charge-gradient doping in promoting efficient C─C coupling.