Journal
ACS APPLIED MATERIALS & INTERFACES
Volume 12, Issue 24, Pages 27682-27690Publisher
AMER CHEMICAL SOC
DOI: 10.1021/acsami.0c03968
Keywords
ceria; metal dopants; hydrogen dissociation; X-ray photoemission spectroscopy; density functional theory; reaction kinetics; surface reduction; silver
Funding
- Universita degli Studi di Modena e Reggio Emilia through the FAR2016 project titled Innovative (oxide-based) materials and methods for fuel cell electrodes implementation
- MIUR through PRIN project [2015CL3APH]
- DoEBES, Division of Chemical Sciences, Geosciences and Biosciences [DESC0007347]
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We investigate the mechanism of H-2 activation on Ag-modified cerium oxide surfaces, of interest for different catalytic applications. The study is performed on thin epitaxial cerium oxide films, investigated by X-ray photoemission spectroscopy to assess the changes of both the Ag oxidation state and the concentration of Ce3+ ions, O vacancies, and hydroxyl groups on the surface during thermal reduction cycles in vacuum and under hydrogen exposure. The results are interpreted using density functional theory calculations to model pristine and Ag-modified ceria surfaces. Although the reactivity of ceria toward H-2 oxidation improves when a fraction of Ce cations is substituted with Ag, the concentration of reduced Ce3+ ions in Ag-modified ceria is found to be lower than in pure ceria under the same conditions. This behavior is observed even though the number of surface oxygen vacancies caused by the thermal treatment under hydrogen exposure is larger for the Ag-modified surface. These results are explained in terms of a change of the oxidation state of the surface Ag, which is able to acquire some of the extra surface electrons created by the oxygen vacancies and the adsorbed hydrogen atoms. Our findings provide new insights into the reactivity of Ag-modified ceria, which has been proposed as a promising alternative to platinum electrodes in electrochemical devices.
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