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Issue 18, 2015
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Surface electrochemistry of CO2 reduction and CO oxidation on Sm-doped CeO2−x: coupling between Ce3+ and carbonate adsorbates

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Abstract

The efficient electro-reduction of CO2 to chemical fuels and the electro-oxidation of hydrocarbons for generating electricity are critical toward a carbon-neutral energy cycle. The simplest reactions involving carbon species in solid-oxide fuel cells and electrolyzer cells are CO oxidation and CO2 reduction, respectively. In catalyzing these reactions, doped ceria exhibits a mixed valence of Ce3+ and Ce4+, and has been employed as a highly active and coking-resistant electrode. Here we report an operando investigation of the surface reaction mechanism on a ceria-based electrochemical cell using ambient pressure X-ray photoelectron spectroscopy. We show that the reaction proceeds via a stable carbonate intermediate, the coverage of which is coupled to the surface Ce3+ concentration. Under CO oxidation polarization, both the carbonate and surface Ce3+ concentration decrease with overpotential. Under CO2 reduction polarization, on the other hand, the carbonate coverage saturates whereas the surface Ce3+ concentration increases with overpotential. The evolution of these reaction intermediates was analyzed using a simplified two-electron reaction scheme. We propose that the strong adsorbate–adsorbate interaction explains the coverage-dependent reaction mechanism. These new insights into the surface electrochemistry of ceria shed light on the optimization strategies for better fuel cell electrocatalysts.

Graphical abstract: Surface electrochemistry of CO2 reduction and CO oxidation on Sm-doped CeO2−x: coupling between Ce3+ and carbonate adsorbates

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Publication details

The article was received on 08 Jan 2015, accepted on 08 Apr 2015 and first published on 09 Apr 2015


Article type: Paper
DOI: 10.1039/C5CP00114E
Citation: Phys. Chem. Chem. Phys., 2015,17, 12273-12281
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    Surface electrochemistry of CO2 reduction and CO oxidation on Sm-doped CeO2−x: coupling between Ce3+ and carbonate adsorbates

    Z. A. Feng, M. L. Machala and W. C. Chueh, Phys. Chem. Chem. Phys., 2015, 17, 12273
    DOI: 10.1039/C5CP00114E

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