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Published February 21, 2017 | Supplemental Material + Published
Journal Article Open

Full atomistic reaction mechanism with kinetics for CO reduction on Cu(100) from ab initio molecular dynamics free-energy calculations at 298 K


A critical step toward the rational design of new catalysts that achieve selective and efficient reduction of CO_2 to specific hydrocarbons and oxygenates is to determine the detailed reaction mechanism including kinetics and product selectivity as a function of pH and applied potential for known systems. To accomplish this, we apply ab initio molecular metadynamics simulations (AIMμD) for the water/Cu(100) system with five layers of the explicit solvent under a potential of −0.59 V [reversible hydrogen electrode (RHE)] at pH 7 and compare with experiment. From these free-energy calculations, we determined the kinetics and pathways for major products (ethylene and methane) and minor products (ethanol, glyoxal, glycolaldehyde, ethylene glycol, acetaldehyde, ethane, and methanol). For an applied potential (U) greater than −0.6 V (RHE) ethylene, the major product, is produced via the Eley–Rideal (ER) mechanism using H_2O + e^–. The rate-determining step (RDS) is C–C coupling of two CO, with ΔG‡ = 0.69 eV. For an applied potential less than −0.60 V (RHE), the rate of ethylene formation decreases, mainly due to the loss of CO surface sites, which are replaced by H*. The reappearance of C_2H_4 along with CH_4 at U less than −0.85 V arises from *CHO formation produced via an ER process of H* with nonadsorbed CO (a unique result). This *CHO is the common intermediate for the formation of both CH_4 and C_2H_4. These results suggest that, to obtain hydrocarbon products selectively and efficiency at pH 7, we need to increase the CO concentration by changing the solvent or alloying the surface.

Additional Information

© 2017 National Academy of Sciences. Edited by Richard Eisenberg, University of Rochester, Rochester, NY, and approved January 5, 2017 (received for review July 22, 2016). Published ahead of print February 6, 2017. This work was fully supported by the Joint Center for Artificial Photosynthesis, a Department of Energy Innovation Hub, supported through the Office of Science of the US Department of Energy under Award DE-SC0004993. This work used the Extreme Science and Engineering Discovery Environment and National Energy Research Scientific Computing Center computing resources. Author contributions: T.C. and W.A.G. designed research; T.C. performed research; T.C., H.X., and W.A.G. analyzed data; and T.C., H.X., and W.A.G. wrote the paper. The authors declare no conflict of interest. This article is a PNAS Direct Submission. This article contains supporting information online at www.pnas.org/lookup/suppl/doi:10.1073/pnas.1612106114/-/DCSupplemental.

Attached Files

Published - PNAS-2017-Cheng-1795-800.pdf

Supplemental Material - pnas.201612106SI.pdf


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