The reactivity of a ceria-rich Ce0.85Zr0.15O2solid solution toward the thermochemical water splitting process (TWS) was studied over repeated H2/H2O redox cycles. The structural and surface modifications after treatment at high temperature under air or N2atmospheres were characterized by high-resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and positron annihilation lifetime spectroscopy (PALS). Samples treated under nitrogen resulted more active due to phase segregation with formation of a zirconyl oxynitride phase in catalytic amount. Insertion of N3-into the structure contributes to an increase in the numbers of oxygen vacancies that preferably arrange in large clusters, and to the stabilization of Ce3+centers on the surface. In comparison, treatment under air resulted in a different arrangement of defects with less Ce3+and smaller and more numerous vacancy clusters. This affects charge transfer and H-coupling processes, which play an important role in boosting the rate of H2production. The behavior is found to be only slightly dependent on the starting ceria-zirconia composition, and it is related to the development of a similar surface heterostructure configuration, characterized by the presence of at least a ceria-rich solid solution and a (cerium-doped) zirconyl oxynitride phase, which is supposed to act as a promoter for TWS reaction. The above findings confirm the importance of a multiphase structure in the design of ceria-zirconia oxides for water splitting reaction and allow a step forward to find an optimal composition. Moreover, the results indicate that doping with nitrogen might be a novel approach for the design of robust, thermally resistant, and redox active materials.

New Insights into the Dynamics That Control the Activity of Ceria-Zirconia Solid Solutions in Thermochemical Water Splitting Cycles

Lucotti, Andrea;
2017-01-01

Abstract

The reactivity of a ceria-rich Ce0.85Zr0.15O2solid solution toward the thermochemical water splitting process (TWS) was studied over repeated H2/H2O redox cycles. The structural and surface modifications after treatment at high temperature under air or N2atmospheres were characterized by high-resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and positron annihilation lifetime spectroscopy (PALS). Samples treated under nitrogen resulted more active due to phase segregation with formation of a zirconyl oxynitride phase in catalytic amount. Insertion of N3-into the structure contributes to an increase in the numbers of oxygen vacancies that preferably arrange in large clusters, and to the stabilization of Ce3+centers on the surface. In comparison, treatment under air resulted in a different arrangement of defects with less Ce3+and smaller and more numerous vacancy clusters. This affects charge transfer and H-coupling processes, which play an important role in boosting the rate of H2production. The behavior is found to be only slightly dependent on the starting ceria-zirconia composition, and it is related to the development of a similar surface heterostructure configuration, characterized by the presence of at least a ceria-rich solid solution and a (cerium-doped) zirconyl oxynitride phase, which is supposed to act as a promoter for TWS reaction. The above findings confirm the importance of a multiphase structure in the design of ceria-zirconia oxides for water splitting reaction and allow a step forward to find an optimal composition. Moreover, the results indicate that doping with nitrogen might be a novel approach for the design of robust, thermally resistant, and redox active materials.
2017
Electronic, Optical and Magnetic Materials; Energy (all); Physical and Theoretical Chemistry; Surfaces, Coatings and Films
File in questo prodotto:
File Dimensione Formato  
New Insights into the Dynamics That Control the Activity of Ceria.pdf

Accesso riservato

: Publisher’s version
Dimensione 5.83 MB
Formato Adobe PDF
5.83 MB Adobe PDF   Visualizza/Apri
11311-1044083_Lucotti.pdf

accesso aperto

: Post-Print (DRAFT o Author’s Accepted Manuscript-AAM)
Dimensione 1.17 MB
Formato Adobe PDF
1.17 MB Adobe PDF Visualizza/Apri

I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.

Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11311/1044083
Citazioni
  • ???jsp.display-item.citation.pmc??? ND
  • Scopus 27
  • ???jsp.display-item.citation.isi??? 26
social impact