We apply in situ environmental transmission electron microscopy (ETEM) to study the dynamic changes taking place during redox reactions in ceria and ceria-zirconia nanoparticles in a hydrogen atmosphere. For pure ceria, we find that a reversible phase transformation takes place at 730 °C in which oxygen vacancies introduced during reduction order to give a cubic superstructure with a periodicity of roughly twice the basic fluorite lattice. We also observe the structural transformations taking place on the surface during reduction in hydrogen. The (1 1 0) ceria surface is initially constructed with a series of low-energy (1 1 1) nanofacets. Under strong reduction, the surface slowly transforms to a smooth (1 1 0) surface which was not observed to change upon re-oxidation. The surface transformation allows the reduced surface to accommodate a high concentration of oxygen vacancies without creating a strong perpendicular dipole moment. In the ceria-zirconia system, we are able to use ETEM to follow the redox activity of individual nanoparticles and correlate this property with structure and composition. We find considerable variation in the redox activity and interpret this in terms of structural differences between the nanoparticles.
- Ceria zirconia
- In situ environmental TEM
ASJC Scopus subject areas
- Electronic, Optical and Magnetic Materials
- Atomic and Molecular Physics, and Optics