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Title: Effects of Electrolyte Buffer Capacity on Surface Reactant Species and the Reaction Rate of CO 2 in Electrochemical CO 2 Reduction

Abstract

In the aqueous electrochemical reduction of CO 2, the choice of electrolyte is responsible for the catalytic activity and selectivity, although there remains a need for more in-depth understanding of electrolyte effects and mechanisms. In this study, using both experimental and simulation approaches, we report how the buffer capacity of the electrolytes affects the kinetics and equilibrium of surface reactant species and the resulting reaction rate of CO 2 with varying partial CO 2 pressure. Electrolytes investigated include KCl (nonbuffered), KHCO 3 (buffered by bicarbonate), and phosphate-buffered electrolytes. Assuming 100% methane production, the simulation successfully explains the experimental trends in maximum CO 2 flux in KCl and KHCO 3 and also highlights the difference between KHCO 3 and phosphate in terms of pKaas well as the impact of the buffer capacity. To examine the electrolyte impact on selectivity, the model is run with a constant total current density. Using this model, several factors are elucidated, including the importance of local pH, which is not in acid/base equilibrium, the impact of buffer identity and kinetics, and the mass-transport boundary-layer thickness. The gained understanding can help to optimize CO 2 reduction in aqueous environments.

Authors:
 [1];  [2];  [3];  [1];  [1];  [3]; ORCiD logo [4]
  1. Panasonic Corporation, Sōraku-gun, Kyoto (Japan). Advanced Research Division
  2. Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States). Joint Center for Artificial Photosynthesis; Univ. of California, Berkeley, CA (United States). Dept. of Chemical and Biomolecular Engineering
  3. California Inst. of Technology (CalTech), Pasadena, CA (United States). Joint Center for Artificial Photosynthesis (JCAP)
  4. Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States). Joint Center for Artificial Photosynthesis
Publication Date:
Research Org.:
Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22). Chemical Sciences, Geosciences & Biosciences Division
OSTI Identifier:
1476629
Grant/Contract Number:  
AC02-05CH11231
Resource Type:
Accepted Manuscript
Journal Name:
Journal of Physical Chemistry. C
Additional Journal Information:
Journal Volume: 122; Journal Issue: 7; Journal ID: ISSN 1932-7447
Publisher:
American Chemical Society
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY

Citation Formats

Hashiba, Hiroshi, Weng, Lien-Chun, Chen, Yikai, Sato, Hiroki K., Yotsuhashi, Satoshi, Xiang, Chengxiang, and Weber, Adam Z. Effects of Electrolyte Buffer Capacity on Surface Reactant Species and the Reaction Rate of CO2 in Electrochemical CO2 Reduction. United States: N. p., 2018. Web. doi:10.1021/acs.jpcc.7b11316.
Hashiba, Hiroshi, Weng, Lien-Chun, Chen, Yikai, Sato, Hiroki K., Yotsuhashi, Satoshi, Xiang, Chengxiang, & Weber, Adam Z. Effects of Electrolyte Buffer Capacity on Surface Reactant Species and the Reaction Rate of CO2 in Electrochemical CO2 Reduction. United States. doi:10.1021/acs.jpcc.7b11316.
Hashiba, Hiroshi, Weng, Lien-Chun, Chen, Yikai, Sato, Hiroki K., Yotsuhashi, Satoshi, Xiang, Chengxiang, and Weber, Adam Z. Fri . "Effects of Electrolyte Buffer Capacity on Surface Reactant Species and the Reaction Rate of CO2 in Electrochemical CO2 Reduction". United States. doi:10.1021/acs.jpcc.7b11316. https://www.osti.gov/servlets/purl/1476629.
@article{osti_1476629,
title = {Effects of Electrolyte Buffer Capacity on Surface Reactant Species and the Reaction Rate of CO2 in Electrochemical CO2 Reduction},
author = {Hashiba, Hiroshi and Weng, Lien-Chun and Chen, Yikai and Sato, Hiroki K. and Yotsuhashi, Satoshi and Xiang, Chengxiang and Weber, Adam Z.},
abstractNote = {In the aqueous electrochemical reduction of CO2, the choice of electrolyte is responsible for the catalytic activity and selectivity, although there remains a need for more in-depth understanding of electrolyte effects and mechanisms. In this study, using both experimental and simulation approaches, we report how the buffer capacity of the electrolytes affects the kinetics and equilibrium of surface reactant species and the resulting reaction rate of CO2 with varying partial CO2 pressure. Electrolytes investigated include KCl (nonbuffered), KHCO3 (buffered by bicarbonate), and phosphate-buffered electrolytes. Assuming 100% methane production, the simulation successfully explains the experimental trends in maximum CO2 flux in KCl and KHCO3 and also highlights the difference between KHCO3 and phosphate in terms of pKaas well as the impact of the buffer capacity. To examine the electrolyte impact on selectivity, the model is run with a constant total current density. Using this model, several factors are elucidated, including the importance of local pH, which is not in acid/base equilibrium, the impact of buffer identity and kinetics, and the mass-transport boundary-layer thickness. The gained understanding can help to optimize CO2 reduction in aqueous environments.},
doi = {10.1021/acs.jpcc.7b11316},
journal = {Journal of Physical Chemistry. C},
number = 7,
volume = 122,
place = {United States},
year = {2018},
month = {2}
}

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