Dual-Element Modulation of Cu Active Sites toward Enhanced C-C Coupling in CO₂ Electroreduction

Electrochemical CO₂ reduction (eCO₂R) on copper (Cu) offers a promising route for producing multicarbon (C₂₊) products but is limited by sluggish C-C coupling kinetics and competing hydrogen evolution. Here, we report a dual-element modulation strategy for directly engineering Cu active sites through the coincorporating boron (B) and gold (Au), yielding a heterostructured Au-B comodified Cu catalyst (AuBDC_h-1) composed of hollow nanocage domains and residual dense nanoparticles. In flow-cell tests with 1 M KOH, AuBDC_h-1 delivers a 3.21-fold higher C₂₊ partial current density (-270.0 ± 26.7 mA cm^-2@-500 mA cm^-2) and a 2.24-fold improvement in cathodic energy efficiency (39.12 ± 4.50%@-400 mA cm^-2) compared with pristine Cu, while effectively suppressing competing hydrogen evolution and methane formation. The catalyst retains its activity in a 5 cm² membrane electrode assembly (MEA), achieving 51.6% C₂₊ selectivity and a C₂₊ partial current density of -154.7 mA cm^-2 at -300 mA cm^-2. In situ Raman spectroscopy reveals that AuBDC_h-1 exhibits an increased *CO_atop/*CO_bridge ratio and a higher fraction of *CO_HFB, establishing a *CO adsorption environment favorable for C-C coupling. In addition, electrochemical CO reduction (eCOR) further confirms its enhanced C-C coupling capability with suppressed protonation to CH₄. Density functional theory (DFT) calculations reveal that this dual modification strengthens *CO binding (-0.70 eV) and reduces the kinetic barrier for C-C bond formation (0.85 eV vs 0.99/1.07 eV for B-only/pristine Cu). Together, these results establish B-Au dual modulation as a robust and transferable design principle for advancing selective CO₂-to-C₂₊ electrolysis.