CO Spillover‐Induced Directed C─C Coupling for CO ₂ Electroreduction to Multicarbon Products

ABSTRACT Efficient CO ₂ ‐to‐multicarbon (C ₂₊ ) electroconversion is constrained by sluggish C─C coupling kinetics dependent on adsorbed *CO availability. We demonstrate that direct interfacial *CO spillover across metal‐metal junctions, replacing conventional tandem CO diffusion, governs C ₂₊ formation on multicomponent Cu‐based catalysts. By engineering CuM (M = Ag, Pd) interfaces with tuned CO‐binding strengths, we establish a quantitative scaling relationship between the *CO spillover rate and C ₂₊ partial current density. The optimized Cu@Ag catalyst promotes rapid *CO transfer from Ag to adjacent Cu sites, lowering the C─C coupling barrier and achieving ∼90% C ₂₊ Faradaic efficiency at 600 mA cm ⁻² in a flow cell. Crucially, cyclic voltammetry under CO and operando attenuated total reflectance surface‐enhanced infrared absorption spectroscopy directly capture dynamic *CO migration and the emergence of *COCHO intermediates, providing explicit experimental evidence for spillover‐driven C─C coupling beyond a conceptual model. These results elevate *CO spillover from a qualitative hypothesis to a measurable design descriptor for building multi‐site interfaces toward efficient, selective, and scalable CO ₂ ‐to‐C ₂₊ electroconversion.