Controlling Speciation during CO₂ Reduction on Cu-Alloy Electrodes

Electrodeposition of Cu, Cu/Ag, and Cu/Sn alloy films by using 3,5-diamino-1,2,4-triazole (DAT) as an electrodeposition inhibitor yields a high surface area Cu-based catalyst. All three Cu-based electrodes exhibit high Faradaic efficiency (FE) of CO₂ reduction toward C₂H₄ production. The CuSn-DAT electrode exhibits the highest FE for CO (∼90% at -0.4 V) and C₂H₄ (∼60% at -0.8 V) production and high current density (∼-225 mA/cm² at -0.8 V). In situ surface enhanced Raman spectroscopy (SERS) studies in a flow cell obtained from the three Cu-based samples show a correlation between the decreased oxide content on the Cu surface, increased presence of CO, and increased activity for CO and C₂ production. The CuSn-DAT electrode has the lowest amount of Cu₂O and exhibits the highest activity, whereas the Cu-DAT electrode has an increasing Cu₂O content and exhibits lower activity as the potential is made negative. These results demonstrate that incorporation of different well-mixed alloy materials provides a way to tune CO₂ reduction speciation.