Pd-Induced Cu Site Differentiation in PdCu/Ag-N-C Catalyst Enables Asymmetric CO─CHO Coupling for Efficient CO-to-CH Conversion.

Electrochemical CO reduction to ethylene (CH) presents a pivotal strategy for industrial decarbonization and carbon valorization but is persistently hindered by the intrinsic high kinetic barrier for symmetric *CO─*CO coupling on conventional Cu catalysts. To surmount this fundamental challenge, we synthesized a tandem PdCu/Ag-N-C catalyst that achieves site differentiation of the surface Cu. The Pd atom induces electronic heterogeneity by creating two electronically distinct Cu sites. The Pd-proximal sites promote *CO protonation to *CHO by leveraging Pd assisted HO dissociation, and Pd-distal sites stabilize *CO. This synergistic division unlocks a highly efficient asymmetric C─CHO coupling pathway. Operando spectroscopy and DFT calculations confirm that the engineered pathway lowers the critical C─C coupling barrier by ∼50%. The PdCu/Ag-N-C catalyst delivers a peak CH Faradaic efficiency of 78.8% (±2.5%) with a partial current density of 441 mA cm at -0.97 V versus RHE in a flow cell, while maintaining excellent operational stability. This work validates asymmetric CO─CHO coupling as a superior route for CH electrosynthesis by introducing a generalizable design paradigm of precisely steering reaction pathways on multi-carbon electrocatalysts.