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Title: Optimizing C–C Coupling on Oxide-Derived Copper Catalysts for Electrochemical CO 2 Reduction

Abstract

Here, copper electrodes, prepared by reduction of oxidized metallic copper, have been reported to exhibit higher activity for the electrochemical reduction of CO 2 and better selectivity toward C 2 and C 3 (C 2+) products than metallic copper that has not been preoxidized. We report here an investigation of the effects of four different preparations of oxide-derived electrocatalysts on their activity and selectivity for CO 2 reduction, with particular attention given to the selectivity to C 2+ products. All catalysts were tested for CO 2 reduction in 0.1 M KHCO 3 and 0.1 M CsHCO 3 at applied voltages in the range from –0.7 to –1.0 V vs RHE. The best performing oxide-derived catalysts show up to ~70% selectivity to C 2+ products and only ~3% selectivity to C 1 products at –1.0 V vs RHE when CsHCO 3 is used as the electrolyte. In contrast, the selectivity to C 2+ products decreases to ~56% for the same catalysts tested in KHCO 3. By studying all catalysts under identical conditions, the key factors affecting product selectivity could be discerned. These efforts reveal that the surface area of the oxide-derived layer is a critical parameter affecting selectivity. A high selectivitymore » to C 2+ products is attained at an overpotential of –1 V vs RHE by operating at a current density sufficiently high to achieve a moderately high pH near the catalyst surface but not so high as to cause a significant reduction in the local concentration of CO 2. On the basis of recent theoretical studies, a high pH suppresses the formation of C 1 relative to C 2+ products. At the same time, however, a high local CO 2 concentration is necessary for the formation of C 2+ products.« less

Authors:
 [1];  [2];  [1]; ORCiD logo [1]; ORCiD logo [1]
  1. Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States); Univ. of California, Berkeley, CA (United States)
  2. Center for High Pressure Science and Technology Advanced Research, Shanghai (People's Republic of China); Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
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:
1418297
Grant/Contract Number:
AC02-05CH11231
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
Journal of Physical Chemistry. C
Additional Journal Information:
Journal Volume: 121; Journal Issue: 26; 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

Lum, Yanwei, Yue, Binbin, Lobaccaro, Peter, Bell, Alexis T., and Ager, Joel W.. Optimizing C–C Coupling on Oxide-Derived Copper Catalysts for Electrochemical CO2 Reduction. United States: N. p., 2017. Web. doi:10.1021/acs.jpcc.7b03673.
Lum, Yanwei, Yue, Binbin, Lobaccaro, Peter, Bell, Alexis T., & Ager, Joel W.. Optimizing C–C Coupling on Oxide-Derived Copper Catalysts for Electrochemical CO2 Reduction. United States. doi:10.1021/acs.jpcc.7b03673.
Lum, Yanwei, Yue, Binbin, Lobaccaro, Peter, Bell, Alexis T., and Ager, Joel W.. 2017. "Optimizing C–C Coupling on Oxide-Derived Copper Catalysts for Electrochemical CO2 Reduction". United States. doi:10.1021/acs.jpcc.7b03673.
@article{osti_1418297,
title = {Optimizing C–C Coupling on Oxide-Derived Copper Catalysts for Electrochemical CO2 Reduction},
author = {Lum, Yanwei and Yue, Binbin and Lobaccaro, Peter and Bell, Alexis T. and Ager, Joel W.},
abstractNote = {Here, copper electrodes, prepared by reduction of oxidized metallic copper, have been reported to exhibit higher activity for the electrochemical reduction of CO2 and better selectivity toward C2 and C3 (C2+) products than metallic copper that has not been preoxidized. We report here an investigation of the effects of four different preparations of oxide-derived electrocatalysts on their activity and selectivity for CO2 reduction, with particular attention given to the selectivity to C2+ products. All catalysts were tested for CO2 reduction in 0.1 M KHCO3 and 0.1 M CsHCO3 at applied voltages in the range from –0.7 to –1.0 V vs RHE. The best performing oxide-derived catalysts show up to ~70% selectivity to C2+ products and only ~3% selectivity to C1 products at –1.0 V vs RHE when CsHCO3 is used as the electrolyte. In contrast, the selectivity to C2+ products decreases to ~56% for the same catalysts tested in KHCO3. By studying all catalysts under identical conditions, the key factors affecting product selectivity could be discerned. These efforts reveal that the surface area of the oxide-derived layer is a critical parameter affecting selectivity. A high selectivity to C2+ products is attained at an overpotential of –1 V vs RHE by operating at a current density sufficiently high to achieve a moderately high pH near the catalyst surface but not so high as to cause a significant reduction in the local concentration of CO2. On the basis of recent theoretical studies, a high pH suppresses the formation of C1 relative to C2+ products. At the same time, however, a high local CO2 concentration is necessary for the formation of C2+ products.},
doi = {10.1021/acs.jpcc.7b03673},
journal = {Journal of Physical Chemistry. C},
number = 26,
volume = 121,
place = {United States},
year = 2017,
month = 7
}

Journal Article:
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  • Selective catalytic reduction of nitrogen oxides (NO/sub x/) is one of the main alternatives for reducing atmospheric pollution produced by NO/sub x/ emissions from static sources. Experimental results described in this paper were carried out in the framework of a more general study undertaken in order to develop an industrial process for the abatement of NO/sub x/ emissions from nitric acid plants. The catalyst used was NiO-CuO/..gamma..lt. slash-Al/sub 2/O/sub 3/ and the reactions studied were NO reduction with NH/sub 3/ (in the presence and absence of oxygen) and NH/sub 3/ oxidation with oxygen, both at atmospheric pressure and in themore » temperature range between 200 and 300/sup 0/C. A kinetic equation was developed by using three different reaction models. This equation fits the experimental results in the above-mentioned temperature range very well, but at high temperatures experimental values clearly deviate from the model predictions. The paper ends by discussing current data in the literature and the experimental evidence obtained in this work in order to postulate a more complex mechanism for the NO reduction with NH/sub 3/ on oxide-supported catalysts. This discussion pointed out possible new lines of research in order to clarify the physical chemistry of the oxidation-reduction system involved in detail.« less
  • Copper(II) oxide catalysts, prepared by non-aqueous adsorption of Cu(acac){sub 2} on Cab-O-Sil followed by thermal decomposition, were titrated by NO and N{sub 2}O to characterize the dispersion of the copper ions. These catalysts showed molar ratios of NO/Cu close to unity when the Cu loadings were less than 2.5 wt%. For samples having loadings greater than 3.8 wt% cu, the NO/CU molar ratios were near 0.7. The NO/Cu molar ratio also depended upon the catalyst preparation technique subsequent to the initial impregnation with Cu(acac){sub 2} when the Cu loadings were {ge} 3.5 wt%. Samples washed with fresh acetonitrile showed NO/Cumore » ratios close to unity, whereas, those not so washed showed NO/Cu ratios near 0.7. IR spectra of NO sorbed on partially decomposed samples showed only bent Cu-N-O, whereas, NO sorbed to the sample which was totally decomposed showed both linear and bent Cu-N-O. Selected samples (3.8 and 8.6 wt% Cu) were reacted with N{sub 2}O to determine the dispersion of the Cu. The sample having 8.6 wt% Cu reacted with the N{sub 2}O to give a dispersion of 0.43; whereas the other sample (3.8 wt%) did not react with the N{sub 2}O. This dispersion determined by N{sub 2}O agreed with that calculated from NO titration (0.47) if the NO/Cu stoichiometry was assumed equal to unity. Subsequently, these catalysts were reduced in H{sub 2} and reoxidized in O{sub 2} to determine the oxidation and reduction kinetics as a function of copper loading. The 3.8 wt% Cu sample lost 1 O/Cu upon reduction in H{sub 2} and gained 1 O/Cu for reoxidation in O{sub 2} for up to five redox cycles; whereas, the 8.6 wt% Cu sample showed a stoichiometry of O/Cu which decreased from 1.00 to 0.57 after five redox cycles.« less