Bromine-Promoted Tandem Catalysis for C₂₊ Production from CO₂ Electroreduction

Renewable energy-driven electrochemical CO₂ reduction holds promise to upgrade CO₂ 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 C₂₊ synthesis. Within this tandem system, AgBr modified Ag nanoparticles, and Cu₂O form a heterogeneous interface. In an alkaline gas-diffusion electrolyzer, the composite catalyst Ag/AgBr/Cu₂O-1 enables highly efficient CO₂-to-C₂₊ conversion, achieving high C₂₊ 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/Cu₂O as well as pure Cu₂O 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 C₂ dimer formation. This work highlights the significance of bromine-mediated tandem catalysis for improving CO₂-to-C₂₊ conversion.