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Title: 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

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). 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 = 0.80more » 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. Therefore, 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.« less
Authors:
 [1] ;  [1] ;  [1]
  1. California Inst. of Technology (CalTech), Pasadena, CA (United States). Joint Center for Artificial Photosynthesis (JCAP) and Materials and Process Simulation Center (MSC)
Publication Date:
Grant/Contract Number:
SC0004993
Type:
Accepted Manuscript
Journal Name:
Journal of the American Chemical Society
Additional Journal Information:
Journal Volume: 138; Journal Issue: 42; Journal ID: ISSN 0002-7863
Publisher:
American Chemical Society (ACS)
Research Org:
California Inst. of Technology (CalTech), Pasadena, CA (United States)
Sponsoring Org:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
OSTI Identifier:
1334328

Cheng, Tao, Xiao, Hai, and Goddard, William A. 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. United States: N. p., Web. doi:10.1021/jacs.6b08534.
Cheng, Tao, Xiao, Hai, & Goddard, William A. 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. United States. doi:10.1021/jacs.6b08534.
Cheng, Tao, Xiao, Hai, and Goddard, William A. 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". United States. doi:10.1021/jacs.6b08534. https://www.osti.gov/servlets/purl/1334328.
@article{osti_1334328,
title = {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},
author = {Cheng, Tao and Xiao, Hai and Goddard, William A.},
abstractNote = {Copper is the only elemental metal that reduces a significant fraction of CO2 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). We carry out QM calculations with an explicit description of water on the Cu(100) surface (experimentally shown to be stable under CO2 reduction reaction conditions) to examine the initial reaction pathways to form CO and formate (HCOO–) from CO2 through free energy calculations at 298 K and pH 7. We find that CO formation proceeds from physisorbed CO2 to chemisorbed CO2 (*CO2δ-), with a free energy barrier of ΔG‡ = 0.43 eV, the rate-determining step (RDS). The subsequent barriers of protonating *CO2δ- 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 CO2 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. Therefore, to alter the product distribution, we need to control this first step of CO2 binding, which might involve controlling pH, alloying, or changing the structure at the nanoscale.},
doi = {10.1021/jacs.6b08534},
journal = {Journal of the American Chemical Society},
number = 42,
volume = 138,
place = {United States},
year = {2016},
month = {10}
}