New aspects of C2 selectivity in electrochemical CO₂ reduction over oxide-derived copper

The electrocatalytic CO₂ reduction to yield C2 products is of particular interest in solar-to-fuel conversion schemes. The nanocrystalline oxide derived copper (ODCu) electrodes are specifically attractive due to their high faradaic efficiency towards C2 hydrocarbons like ethylene, ethane, acetate and ethanol. However, the mechanistic understanding of this special selectivity is still an impediment. In this work, ODCu is obtained from Cu₂O nanowires and employed for electrocatalytic CO₂ reduction, during which ethylene is found to be the major product with a faradaic efficiency of 65% at -0.8 V (vs. RHE). By in situ photoresponse measurement, combined with the ex situ structure and composition analysis, Cu₂O is demonstrated to be persistent on the surface of ODCu throughout the CO₂ reduction reaction (CO₂RR) even at high applied bias (-1.0 V vs. RHE), while Cu₂O is not present on the bulk Cu foil. Density functional theory calculations are employed to further investigate the correlation between the surface Cu₂O on ODCu and its C2 selectivity performance, which is attributed to the orbital interactions between the persistent oxide and CO₂ reduction intermediates. It should be noted that uncovering the active sites is the initial step to understand the surface reaction chemistry in CO₂RR; here, we propose that the presence of Cu₂O is the key for C2 selectivity during CO₂RR in the ODCu system, which may facilitate the development of highly efficient catalysts.