Mechanism for spontaneous oxygen and hydrogen evolution reactions on CoO nanoparticles
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c8ta11087e.pdf
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1.19 MB
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Checksum (MD5)
0098b26e247b9a433e4633aa2a441ce9
Author(s)
Park, Kyoung-Won
Kolpak, Alexie M.
Date Issued
February 2019
Journal
Journal of Materials Chemistry A
Publisher
Royal Society of Chemistry
Citation
Park, Kyoung-Won, and Alexie M. Kolpak. “Mechanism for Spontaneous Oxygen and Hydrogen Evolution Reactions on CoO Nanoparticles.” Journal of Materials Chemistry A, 2019.
Version
Final published version
Abstract
Overall photocatalytic water splitting with a high efficiency of ~5% has recently been observed for CoO nanoparticle suspensions in the absence of an applied bias or co-catalyst. Although experimental measurements indicate that the overall photocatalytic water splitting is caused by optimal band edge alignments with respect to the redox potentials of water, the mechanism by which H[subscript 2] and O[subscript 2] simultaneously evolve on these nanoparticles is unknown. In this study, we used first-principles density functional theory (DFT) calculations to elucidate the mechanisms for the charge separation and H[subscript 2] and O[subscript 2] evolution on CoO nanoparticles under illumination in aqueous solution. We demonstrated that electrons are driven to the CoO(100) facet and holes are driven to the hydroxylated CoO(111) facet (OH*–CoO(111)) as a result of the built-in potential arising from the difference in the band edge positions on the two facets. Furthermore, based on a set of criteria, depending on if the photoexcited electrons and holes have sufficient energy to overcome the kinetic barrier along the H[subscript 2] and O[subscript 2] evolution
reaction pathways, respectively, on the relevant surface facet, we show that H2 evolution preferentially occurs on the CoO(100) facet, while O[subscript 2] evolution occurs on the OH*–CoO(111) surface. Our understanding of the overall water splitting mechanism on CoO nanoparticles provides a general explanation for the experimentally observed overall water splitting phenomena on a variety of selfstanding photocatalysts, including g-Ga2O[subscript 3], Cu[subscript 2]O, and KTaO[subscript 3], without an external driving potential or co-catalyst. In addition, we provide a new strategy for designing novel photocatalysts with high efficiency by controlling their surface configurations and morphologies.
MIT Department
Massachusetts Institute of Technology. Department of Materials Science and Engineering
Massachusetts Institute of Technology. Department of Mechanical Engineering
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Creative Commons Attribution Noncommercial 3.0 unported license
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DOI of Published Version
https://doi.org/10.1039/C8TA11087E
