Bromine‐Promoted Tandem Catalysis for C ₂₊ Production from CO ₂ Electroreduction

ABSTRACT Renewable energy‐driven electrochemical CO ₂ reduction holds promise to upgrade CO ₂ into high‐value‐added multicarbon fuels and chemicals. However, achieving satisfactory selectivity on Cu catalysts poses a grand challenge because of the sluggish C─C coupling and competitive balance between adsorbed intermediates. Herein, in this work, a distinct type of bromine‐mediated Ag─Cu heterogeneous tandem catalyst, is rationally designed by integrating synergistic sites to promote enhanced *CO accumulation and its protonation for subsequent coupling for C ₂₊ synthesis. Within this tandem system, AgBr modified Ag nanoparticles, and Cu ₂ O form a heterogeneous interface. In an alkaline gas‐diffusion electrolyzer, the composite catalyst Ag/AgBr/Cu ₂ O‐1 enables highly efficient CO ₂ ‐to‐C ₂₊ conversion, achieving high C ₂₊ production with a highest Faradaic efficiency of 82.7% and a partial current density of 168.2 mA·cm ^{− 2} , which outperforms both physically mixed Ag/Cu ₂ O as well as pure Cu ₂ O counterparts. By using electrochemical in situ Fourier transform infrared (FTIR) spectroscopy, we find that our bromine‐promoted tandem catalyst significantly increases both *CO and *CHO coverage on the surface for triggering asymmetric C–C coupling. Density functional theory (DFT) calculations further disclose energetically favorable *CO–*CHO coupling route for C ₂ dimer formation. This work highlights the significance of bromine‐mediated tandem catalysis for improving CO ₂ ‐to‐C ₂₊ conversion.