CO₂ reduction on pure Cu produces only H₂ after subsurface O is depleted: Theory and experiment

• Published in: Proceedings of the National Academy of Sciences - PNAS 2021-06, Vol.118 (23), p.1-8
• Main Authors: Liu, Guiji, Lee, Michelle, Kwon, Soonho, Zeng, Guosong, Eichhorn, Johanna, Buckley, Aya K., Toste, F. Dean, Goddard, William A., Toma, Francesca M.
• Format: Article
• Language: English
• Subjects: Carbon dioxide; Catalysts; Copper; Density functional theory; Electrocatalysts; Ethylene; Hydrogen evolution; Hydrogen production; Oxygen; Physical Sciences; Reaction time; Reduction; Time dependence
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.2012649118

We elucidate the role of subsurface oxygen on the production of C₂ products from CO₂ reduction over Cu electrocatalysts using the newly developed grand canonical potential kinetics density functional theory method, which predicts that the rate of C₂ production on pure Cu with no O is ∼500 times slower than H₂ evolution. In contrast, starting with Cu₂O, the rate of C₂ production is >5,000 times faster than pure Cu(111) and comparable to H₂ production. To validate these predictions experimentally, we combined time-dependent product detection with multiple characterization techniques to show that ethylene production decreases substantially with time and that a sufficiently prolonged reaction time (up to 20 h) leads only to H₂ evolution with ethylene production ∼1,000 times slower, in agreement with theory. This result shows that maintaining substantial subsurface oxygen is essential for long-term C₂ production with Cu catalysts.