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

Abstract

Here, a critical step toward the rational design of new catalysts that achieve selective and efficient reduction of CO₂ 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 H₂O + 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 C₂H₄ along with CH₄ at U less than –0.85 V arises from *CHO formationmore » produced via an ER process of H* with nonadsorbed CO (a unique result). This *CHO is the common intermediate for the formation of both CH₄ and C₂H₄. 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.« less

Authors:

Cheng, Tao  ^[1];

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• Search DOE PAGES for ORCID "0000-0003-4830-177X"

Xiao, Hai  ^[1];

• Search DOE PAGES for author "Xiao, Hai"
• Search DOE PAGES for ORCID "0000-0001-9399-1584"

Goddard, III, William A.  ^[1]

• Search DOE PAGES for author "Goddard, III, William A."
• Search DOE PAGES for ORCID "0000-0003-0097-5716"

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1. Joint Center for Artificial Photosynthesis, California Institute of Technology, Pasadena, CA 91125,, Materials and Process Simulation Center (MC139-74), California Institute of Technology, Pasadena, CA 91125

Publication Date:

Mon Feb 06 00:00:00 EST 2017

Research Org.:

California Institute of Technology (CalTech), Pasadena, CA (United States)

Sponsoring Org.:

USDOE Office of Science (SC)

OSTI Identifier:

1342801

Alternate Identifier(s):

OSTI ID: 1464954

Grant/Contract Number:  

SC0004993

Resource Type:

Published Article

Journal Name:

Proceedings of the National Academy of Sciences of the United States of America

Additional Journal Information:

Journal Name: Proceedings of the National Academy of Sciences of the United States of America Journal Volume: 114 Journal Issue: 8; Journal ID: ISSN 0027-8424

Publisher:

Proceedings of the National Academy of Sciences

Country of Publication:

United States

Language:

English

Subject:

36 MATERIALS SCIENCE; reaction mechanism; electrocatalysis; copper; QM metadynamics; free-energy reaction barriers