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Reaction Mechanisms for the Electrochemical Reduction of CO_2 to CO and Formate on the Cu(100) Surface at 298 K from Quantum Mechanics Free Energy Calculations with Explicit Water

Cheng, Tao and Xiao, Hai and Goddard, William A., III (2016) Reaction Mechanisms for the Electrochemical Reduction of CO_2 to CO and Formate on the Cu(100) Surface at 298 K from Quantum Mechanics Free Energy Calculations with Explicit Water. Journal of the American Chemical Society, 138 (42). pp. 13802-13805. ISSN 0002-7863. https://resolver.caltech.edu/CaltechAUTHORS:20161021-102228722

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Abstract

Copper is the only elemental metal that reduces a significant fraction of CO_2 to hydrocarbons and alcohols, but the atomistic reaction mechanism that controls the product distributions is not known because it has not been possible to detect the reaction intermediates on the electrode surface experimentally, or to carry out Quantum Mechanics (QM) calculations with a realistic description of the electrolyte (water). Here, we carry out QM calculations with an explicit description of water on the Cu(100) surface (experimentally shown to be stable under CO_2 reduction reaction conditions) to examine the initial reaction pathways to form CO and formate (HCOO–) from CO_2 through free energy calculations at 298 K and pH 7. We find that CO formation proceeds from physisorbed CO_2 to chemisorbed CO_2 (*CO_2^(δ−)), with a free energy barrier of ΔG⧧ = 0.43 eV, the rate-determining step (RDS). The subsequent barriers of protonating *CO_2^(δ−) to form COOH* and then dissociating COOH* to form *CO are 0.37 and 0.30 eV, respectively. HCOO– formation proceeds through a very different pathway in which physisorbed CO_2 reacts directly with a surface H* (along with electron transfer), leading to ΔG⧧ = 0.80 eV. Thus, the competition between CO formation and HCOO– formation occurs in the first electron-transfer step. On Cu(100), the RDS for CO formation is lower, making CO the predominant product. Thus, to alter the product distribution, we need to control this first step of CO_2 binding, which might involve controlling pH, alloying, or changing the structure at the nanoscale.


Item Type:Article
Related URLs:
URLURL TypeDescription
http://dx.doi.org/10.1021/jacs.6b08534DOIArticle
http://pubs.acs.org/doi/suppl/10.1021/jacs.6b08534PublisherSupporting Information
ORCID:
AuthorORCID
Cheng, Tao0000-0003-4830-177X
Xiao, Hai0000-0001-9399-1584
Goddard, William A., III0000-0003-0097-5716
Additional Information:© 2016 American Chemical Society. Received: August 17, 2016. Publication Date (Web): October 11, 2016. This work was fully supported by the Joint Center for Artificial Photosynthesis, a DOE Energy Innovation Hub, supported through the Office of Science of the U.S. Department of Energy under Award No. DE-SC0004993. We thank Mr. Yufeng Huang, Dr. Ravishankar Sundararaman, Dr. Robert J. Nielsen, and Prof. Manuel P. Soriaga for helpful discussions. The calculations were carried out mostly on the Zwicky (Caltech) astrophysics computing system [using funding from NSF (CBET 1512759)], with some on NERSC. The authors declare no competing financial interest.
Group:JCAP
Funders:
Funding AgencyGrant Number
Department of Energy (DOE)DE-SC0004993
NSFCBET-1512759
Issue or Number:42
Record Number:CaltechAUTHORS:20161021-102228722
Persistent URL:https://resolver.caltech.edu/CaltechAUTHORS:20161021-102228722
Official Citation:Reaction Mechanisms for the Electrochemical Reduction of CO2 to CO and Formate on the Cu(100) Surface at 298 K from Quantum Mechanics Free Energy Calculations with Explicit Water Tao Cheng, Hai Xiao, and William A. Goddard III Journal of the American Chemical Society 2016 138 (42), 13802-13805 DOI: 10.1021/jacs.6b08534
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:71337
Collection:CaltechAUTHORS
Deposited By: Tony Diaz
Deposited On:21 Oct 2016 18:53
Last Modified:16 Apr 2020 23:07

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