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A DEMS Study of the Reduction of CO_2, CO, and HCHO Pre-Adsorbed on Cu Electrodes: Empirical Inferences on the CO_2RR Mechanism

Javier, Alnald and Chmielowiec, Brian and Sanabria-Chinchilla, Jean and Kim, Youn-Geun and Baricuatro, Jack H. and Soriaga, Manuel P. (2015) A DEMS Study of the Reduction of CO_2, CO, and HCHO Pre-Adsorbed on Cu Electrodes: Empirical Inferences on the CO_2RR Mechanism. Electrocatalysis, 6 (2). pp. 127-131. ISSN 1868-2529. https://resolver.caltech.edu/CaltechAUTHORS:20150202-141003348

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Abstract

The effective abatement of atmospheric carbon through its conversion via electrochemical reduction to pure and oxygenated hydrocarbon fuels relies on the ability to control product selectivity at viable current densities and faradaic efficiencies. One critical aspect is the choice of the electrode and, in the CO_2-reduction electrocatalyst landscape, copper sits as the only metal known to deliver a remarkable variety of reduction products other than carbon monoxide and formic acid. However, much better catalyst performance is needed. The overall energy efficiency of copper is less than 40 %, and its nominal overvoltage at benchmark current densities remains unacceptably large at ca. 1 V. The diversity of the product distribution also becomes a major inconvenience in the likelihood that only one product is desired; unless, of course, if the selectivity window for such product is already known. Several experimental parameters influence the product selectivity of the CO_2 reduction reactions (hereafter referred to as CO_2RR); the more obvious include the composition and the crystal structure of the catalyst surface, the applied potential, the solution pH, and the supporting electrolyte. The documentation, at the atomic level, of the mechanistic origins of the CO_2RR selectivity of copper demands a systematic combination of ex situ, in situ, and operando techniques to interrogate the electrode surface, pristine and modified, prior to, during, and after the reduction reaction; the task includes not only the analysis of reaction-product distributions but also the identification of surface intermediates that serve as the precursor states for each reaction pathway. We recently studied the nature of well-defined Cu(hkl) single-crystal surfaces that, similar to “real-world” catalysts, were handled in air. Such investigation is pertinent since Cu is a well-known scavenger of molecular oxygen; hence, CO_2RR electrocatalysis must first contend with the initial presence of multilayers of disordered copper oxides. It was found that the oxides are actually easily reduced electrochemically back to the metal; in addition, even if the oxided single-crystal surface is severely disordered, cathodic reduction completely regenerates the original ordered structure. Most recently, we discovered that a polycrystalline Cu electrode held at a fixed negative potential in the CO_2RR region in KOH, undergoes stepwise surface reconstruction, first to Cu(111) and then to Cu(100). The results help explain the Cu(100)-like behavior of Cu(pc) in terms of CO_2RR product selectivity. In the work described in this Letter, we have applied differential electrochemical mass spectrometry (DEMS) of pre-adsorbed reactants and intermediates as a complementary experimental approach in the study of the mechanistic pathways for the Cu-catalyzed CO_2 reduction reactions; the reactant was CO_2 and the intermediates were CO and HCHO. The reduction products monitored by mass spectrometry were H_2, CO (from CO_2), CH_4, H_2C=CH_2 and CH_3CH_2OH.


Item Type:Article
Related URLs:
URLURL TypeDescription
http://dx.doi.org/10.1007/s12678-015-0246-1DOIArticle
http://link.springer.com/article/10.1007%2Fs12678-015-0246-1PublisherArticle
http://rdcu.be/oZq3PublisherFree ReadCube access
ORCID:
AuthorORCID
Javier, Alnald0000-0002-0306-5462
Kim, Youn-Geun0000-0002-5936-6520
Soriaga, Manuel P.0000-0002-0077-6226
Additional Information:© 2015 Springer Science+Business Media New York. Published online 27 Jan 2015. This material is based upon work performed by the Joint Center for Artificial Photosynthesis, a DOE Energy Innovation Hub, supported through the Office of Science of the US Department of Energy under Award No. DE-SC0004993.
Group:JCAP
Funders:
Funding AgencyGrant Number
Department of Energy (DOE)DE-SC0004993
Issue or Number:2
Record Number:CaltechAUTHORS:20150202-141003348
Persistent URL:https://resolver.caltech.edu/CaltechAUTHORS:20150202-141003348
Official Citation:Javier, A., Chmielowiec, B., Sanabria-Chinchilla, J. et al. Electrocatalysis (2015) 6: 127. doi:10.1007/s12678-015-0246-1
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:54306
Collection:CaltechAUTHORS
Deposited By: Ruth Sustaita
Deposited On:03 Feb 2015 21:18
Last Modified:09 Mar 2020 13:18

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