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  4. Contrasting Views of the Electric Double Layer in Electrochemical CO2 Reduction: Continuum Models vs Molecular Dynamics
 
research article

Contrasting Views of the Electric Double Layer in Electrochemical CO2 Reduction: Continuum Models vs Molecular Dynamics

Johnson, Evan Fair  
•
Haussener, Sophia  
June 14, 2024
Journal Of Physical Chemistry C

In the field of electrochemical CO2 reduction, both continuum models and molecular dynamics (MD) models have been used to understand the electric double layer (EDL). MD often focuses on the region within a few nm of the electrode, while continuum models can span up to the device level (cm). Still, both methods model the EDL, and for a cohesive picture of the CO2 electrolysis system, the two methods should agree in the regions where they overlap length scales. To this end, we make a direct comparison between state-of-the-art continuum models and classical MD simulations under the conditions of CO2 reduction on a Ag electrode. For continuum modeling, this includes the Poisson-Nernst-Planck formulation with steric (finite ion size) effects, and in MD the electrode is modeled with the constant potential method. The comparison yields numerous differences between the two modeling methods. MD shows cations forming two adsorbed layers, including a fully hydrated outer layer and a partial hydration layer closer to the electrode surface. The strength of the inner adsorbed layer increases with cation size (Li+ < Na+ < K+ < Cs+) and with more negative applied potentials. Continuum models that include steric effects predict CO2 to be mostly excluded within 1 nm of the cathode due to tightly packed cations, yet we find little evidence to support these predictions from the MD results. In fact, MD shows that the concentration of CO2 increases within a few & Aring; of the cathode surface due to interactions with the Ag electrode, a factor not included in continuum models. The EDL capacitance is computed from the MD results, showing values in the range of 7-9 mu F cm(-2), irrespective of the electrolyte concentration, cation identity, or applied potential. The direct comparison between the two modeling methods is meant to show the areas of agreement and disagreement between the two views of the EDL, so as to improve and better align these models.

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Type
research article
DOI
10.1021/acs.jpcc.4c03469
Web of Science ID

WOS:001249994000001

Author(s)
Johnson, Evan Fair  
Haussener, Sophia  
Date Issued

2024-06-14

Publisher

Amer Chemical Soc

Published in
Journal Of Physical Chemistry C
Volume

128

Issue

25

Start page

10450

End page

10464

Subjects

Physical Sciences

•

Technology

•

Carbon-Dioxide

•

Silver

•

Electrolytes

•

Simulations

•

Capacitance

•

Contact

•

Water

Editorial or Peer reviewed

REVIEWED

Written at

EPFL

EPFL units
LRESE  
FunderGrant Number

NCCR Catalysis

180544

National Centre of Competence in Research - Swiss National Science Foundation

Available on Infoscience
July 3, 2024
Use this identifier to reference this record
https://infoscience.epfl.ch/handle/20.500.14299/209116
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