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.