Compositional and Geometrical Effects of Bimetallic Cu–Sn Catalysts on Selective Electrochemical CO₂ Reduction to CO

Electrochemical reduction of carbon dioxide (CO2) is a promising method toward carbon recycling. Highly selective bimetallic catalysts have been extensively demonstrated, while efforts to understand the compositional and geometrical effects have been limited. Here, we studied the relationship between the catalytic activity of bimetallic Cu–Sn catalysts with their composition and geometry through the fabrication of three-dimensional hierarchical (3D-h) Cu nanostructure and the solution-based coating of Sn nanoparticles (NPs). As the coating time of Sn NPs was increased from 1 to 60 s, Sn NPs with a larger size and a higher surface density were coated onto the 3D-h Cu, thus the surface atomic ratio of Cu/Sn gradually decreased. This compositional change in bimetallic Cu–Sn catalysts remarkably shifted the faradaic efficiency (FE) of carbon monoxide (CO) from 90.0 to 23.4% at −0.6 VRHE. Moreover, we found that the catalytic performance increases as the geometric structure becomes complex in the order of flat, rods, and 3D-h Cu–Sn. The 3D-h Cu–Sn began to produce CO at a low potential of −0.15 VRHE and showed the maximum FECO of 98.6% at −0.45 VRHE. This study reveals that the synergetic effects of composition and nanoscale geometry are significant for the CO2 reduction reaction.