Evidence of Local Corrosion of Bimetallic Cu–Sn Catalysts and Its Effects on the Selectivity of Electrochemical CO₂ Reduction

The electrochemical carbon dioxide (CO2) reduction is a promising method for carbon recycling. Bimetallic catalysts have been extensively developed for the selective production of carbon monoxide (CO) and formate (HCOOH), while efforts to understand the change in structure and composition under reaction conditions have been limited. Here, we provided experimental evidence for the local corrosion phenomenon of bimetallic Cu–Sn catalysts through the patterning of the Sn layer on Cu foil (Cu/p-Sn). The surface composition and morphology of Cu/p-Sn 3 nm catalysts spontaneously changed during the reaction in CO2-purged 0.1 M KHCO3 electrolyte. The Sn patterns became thinner, and the Sn elements were migrated to the outside of the patterns. Consequently, the Cu/p-Sn catalysts exhibited a unique catalytic selectivity of high CO faradaic efficiency (FECO) of 58.1% at −1.0 VRHE, which cannot be obtained from the bulk Cu (FECO = 7.5%) and Cu/Sn catalysts without the Sn pattern (FEHCOOH = 90.6%). Moreover, the catalytic selectivity of the Cu/p-Sn catalysts shifted from CO to HCOOH as the thickness of the Sn pattern increased from 3 to 50 nm. This study sheds light on the origin of the local corrosion of bimetallic catalysts and its effect on the catalytic selectivity of CO2 reduction.