Subsurface oxide plays a critical role in CO₂ activation by Cu(111) surfaces to form chemisorbed CO₂, the first step in reduction of CO₂
A national priority is to convert CO₂ into high-value chemical products such as liquid fuels. Because current electrocatalysts are not adequate, we aim to discover new catalysts by obtaining a detailed understanding of the initial steps of CO₂ electroreduction on copper surfaces, the best current catalysts. Using ambient pressure X-ray photoelectron spectroscopy interpreted with quantum mechanical prediction of the structures and free energies, we show that the presence of a thin suboxide structure below the copper surface is essential to bind the CO₂ in the physisorbed configuration at 298 K, and we show that this suboxide is essential for converting to the chemisorbed CO₂ in the presence of water as the first step toward CO₂ reduction products such as formate and CO. This optimum suboxide leads to both neutral and charged Cu surface sites, providing fresh insights into how to design improved carbon dioxide reduction catalysts.
© 2017 National Academy of Sciences. Freely available online through the PNAS open access option. Contributed by William A. Goddard III, May 9, 2017 (sent for review January 26, 2017; reviewed by Charles T. Campbell and Bruce E. Koel). This work was supported through the Office of Science, Office of Basic Energy Science (BES), of the US Department of Energy (DOE) under Award DE-SC0004993 to the Joint Center for Artificial Photosynthesis and as part of the Joint Center for Energy Storage Research, DOE Energy Innovation Hubs. The Advanced Light Source is supported by the Director, Office of Science, Office of BES, of the US DOE under Contract DE-AC02-05CH11231. The QM calculations were carried out on the Zwicky supercomputer at Caltech. M.F. and H.X. contributed equally to this work. Author contributions: M.F., H.X., T.C., W.A.G., J.Y., and E.J.C. designed research, performed research, analyzed data, and wrote the paper. Reviewers: C.T.C., University of Washington; and B.E.K., Princeton University. The authors declare no conflict of interest. This article contains Supporting Information online at www.pnas.org/lookup/suppl/doi:10.1073/pnas.1701405114/-/DCSupplemental.
Published - PNAS-2017-Favaro-6706-11.pdf
Supplemental Material - pnas.201701405SI.pdf