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    Establishing efficient cobalt based catalytic sites for oxygen evolution on a Ta3N5 photocatalyst

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    acs2Echemmater2E5b02139.pdf
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    Type
    Article
    Authors
    Nurlaela, Ela cc
    Ould-Chikh, Samy cc
    Llorens, Isabelle
    Hazemann, Jean-louis
    Takanabe, Kazuhiro cc
    KAUST Department
    Catalysis for Energy Conversion (CatEC)
    Chemical Engineering Program
    Chemical Science Program
    KAUST Catalysis Center (KCC)
    Physical Science and Engineering (PSE) Division
    Date
    2015-08-13
    Online Publication Date
    2015-08-13
    Print Publication Date
    2015-08-25
    Permanent link to this record
    http://hdl.handle.net/10754/565796
    
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    Abstract
    In a photocatalytic suspension system with a powder semiconductor, the interface between the photocatalyst semiconductor and catalyst should be constructed to minimize resistance for charge transfer of excited carriers. This study demonstrates an in-depth understanding of pretreatment effects on the photocatalytic O2 evolution reaction (OER) activity of visible-light-responsive Ta3N5 decorated with CoOx nanoparticles. The CoOx/Ta3N5 sample was synthesized by impregnation followed by sequential heat treat-ments under NH3 flow and air flow at various temperatures. Various characterization techniques, including X-ray diffraction (XRD), X-ray absorption spectroscopy (XAS), scanning transmission electron microscopy (STEM), and X-ray photoelectron spec-troscopy (XPS), were used to clarify the state and role of cobalt. No improvement in photocatalytic activity for OER over the bare Ta3N5 was observed for the as-impregnated CoOx/Ta3N5, likely because of insufficient contact between CoOx and Ta3N5. When the sample was treated in NH3 at high temperature, a substantial improvement in the photocatalytic activity was observed. After NH3 treatment at 700 °C, the Co0-CoOx core-shell agglomerated cobalt structure was identified by XAS and STEM. No metallic cobalt species was evident after the photocatalytic OER, indicating that the metallic cobalt itself is not essential for the reaction. Accordingly, mild oxidation (200 °C) of the NH3-treated CoOx/Ta3N5 sample enhanced photocatalytic OER activity. Oxidation at higher temperatures drastically eliminated the photocatalytic activity, most likely because of unfavorable Ta3N5 oxidation. These results suggest that the intimate contact between cobalt species and Ta3N5 facilitated at high temperature is beneficial to enhancing hole transport and that the cobalt oxide provides electrocatalytic sites for OER.
    Citation
    Establishing efficient cobalt based catalytic sites for oxygen evolution on a Ta3N5 photocatalyst 2015:150805135245001 Chemistry of Materials
    Publisher
    American Chemical Society (ACS)
    Journal
    Chemistry of Materials
    DOI
    10.1021/acs.chemmater.5b02139
    Additional Links
    http://pubs.acs.org/doi/abs/10.1021/acs.chemmater.5b02139
    ae974a485f413a2113503eed53cd6c53
    10.1021/acs.chemmater.5b02139
    Scopus Count
    Collections
    Articles; Physical Science and Engineering (PSE) Division; Chemical Science Program; Chemical Engineering Program; KAUST Catalysis Center (KCC)

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