Electrical and oxygen storage/release properties of nanocrystalline ceria-zirconia solid solutions

The electrical properties of nanocrystalline Ce0.75Zr0.25O2 solid solution in the ceria-zirconia system were investigated using four-point DC conductivity measurements and impedance spectroscopy. Conductivity measurements were carried out as a function of temperature (723-821 K) and oxygen partial pressure (pO2 = 10-3 - 1 atm). The results were compared to the properties of bulk oxide of similar composition. Both the nanocrystalline and the coarsened oxide exhibit mixed conduction where the prevailing contribution is electronic. However, the nanocrystalline oxide shows a higher ionic contribution due to the enhancement of anionic vacancy mobility, which is more than one order of magnitude higher. In contrast with pure ceria, the electronic conductivity and activation energy for diffusion is similar in both nanocrystalline and sintered material, which could explain the similar reduction behavior shown by high and low surface area samples. These results are discussed and interpreted in terms of the role of surface area and the related crystallite size in the catalytic and reduction properties of ceria-zirconia solid solutions.