Tunable Selectivity for Electrochemical CO₂Reduction by Bimetallic Cu-Sn Catalysts: Elucidating the Roles of Cu and Sn

Production of formate or CO from electrochemical CO₂reduction reactions (eCO₂RRs) represents a promising way to utilize CO₂with future low-carbon electricity to produce value-added chemicals and fuels. Herein, a series of Cu-Sn composite catalysts were designed for eCO₂RRs. The reduction products could be tuned selectively from formate to CO by varying the Cu/Sn composition. The catalyst Cu₁Sn₁with a CuSn alloy core and a SnO shell structure doped with a small amount of Cu gives a maximum faradic efficiency (FE) of 95.4 for formate at −1.2 V. In contrast, the single-Sn-atom-doped Cu of Cu₂₀Sn₁is selective to CO with a maximum FE of 95.3% at −1.0 V. The DFT results reveal that the existence of small amounts of Cu or Sn single atoms in these two catalysts is critical to reducing the reaction free energies of CO₂reduction, resulting in the selective formation of formate and CO, respectively.