Stability of Ultrathin Ceria Films on Pt(111) Exposed to Air and Treated in Redox Cycles

Abstract : The stability of cerium oxide (ceria) is a major topic in the field of heterogeneous catalysis. When exposed to a reactive environment or treated in a redox step, ceria is prone to changes of its surface morphology, atomic structure, and composition, with a strong impact onto its catalytic properties. Here, we investigate the stability of Pt(111)-supported ultrathin ceria films upon air exposure and during redox cycles under ultrahigh vacuum (UHV) conditions. Scanning probe microscopy, X-ray photoemission spectroscopy, and low-energy electron diffraction show that upon air exposure, a clean ceria film surface gets contaminated by hydroxyls and carbon-containing species whereas a following annealing in molecular oxygen at around 650 °C removes such contaminants and allows to restore the original surface morphology and structure. When clean films are oxidized in a background oxygen pressure (reduced in UHV) at ∼650 °C, the film coverage increases (decreases). The decrease of the film coverage upon reduction is probably due to a release of cerium atoms, which form an alloy with the platinum substrate that acts as a reservoir for cerium atoms. Due to the alloying, the surface work function (WF) of Pt(111) decreases by ΔϕCePt5/Pt-Pt ≈ −0.20 ± 0.05 eV, as observed by Kelvin probe force microscopy. Upon oxidation, the released cerium is used to form new ceria. With respect to WF changes of the Pt(111) surface by the ceria film, a decrease is found for the oxidized film (ΔϕCeO2/Pt-Pt ≈ −0.55 ± 0.05 eV) as well as for the reduced film (ΔϕrCeria/Pt-Pt ≈ −0.60 ± 0.05 eV).
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Journal of Physical Chemistry C, American Chemical Society, 2018, 122 (45), pp.25954-25963. 〈10.1021/acs.jpcc.8b07231〉
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Soumis le : mercredi 7 novembre 2018 - 10:44:48
Dernière modification le : jeudi 15 novembre 2018 - 16:42:52

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Gabriele Gasperi, Paola Luches, Clemens Barth. Stability of Ultrathin Ceria Films on Pt(111) Exposed to Air and Treated in Redox Cycles. Journal of Physical Chemistry C, American Chemical Society, 2018, 122 (45), pp.25954-25963. 〈10.1021/acs.jpcc.8b07231〉. 〈hal-01914683〉

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