Abstract

  Electrochemical CO_​2 reduction (eCO_​2R) on copper (Cu) offers a promising route for producing multicarbon (C_​2+) 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 (AuBDCh^​-1) composed of hollow nanocage domains and residual dense nanoparticles. In flow-cell tests with 1 M KOH, AuBDCh^​-1 delivers a 3.21-fold higher C_​2+ 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 cm^​2 membrane electrode assembly (MEA), achieving 51.6% C_​2+ selectivity and a C_​2+ partial current density of −154.7 mA cm^​-2 at −300 mA cm^​-2. In situ Raman spectroscopy reveals that AuBDCh^​-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 CH_​4. 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 CO_​2-to-C_​2+ electrolysis.