Doped ceria-zirconia

Tenibile, D., TrovareUi, A., de Leitenburg, C., Primavera, A., and Giutiano, G. Catal54ic combustion of hydrocarbons with Mn and Cu-doped ceria-zirconia solid solutions. Catal Today 1999, 47, 133-140. 

The most efficient electrodes for SOFC are usually composites comprised of perovskites and oxygen-conducting electrolytes (doped ceria, zirconia etc) as only composite materials can meet the most of requirements for proper functioning of the electrode. For SOFC cathodes, main requirements are [3]... 

Active heterogeneous catalysts have been obtained. Examples include titania-, vanadia-, silica-, and ceria-based catalysts. A survey of catalytic materials prepared in flames can be found in [20]. Recent advances include nanocrystalline Ti02 [24], one-step synthesis of noble metal Ti02 [25], Ru-doped cobalt-zirconia [26], vanadia-titania [27], Rh-Al203 for chemoselective hydrogenations [28], and alumina-supported noble metal particles via high-throughput experimentation [29]. 

For zirconia-doped ceria it was shown that redox cycling can enhance the oxygen storage capacity, see F. Fally, V. Perrichon, H. Vidal, J. Kaspar, G. Blanco, J. M. Pintado, S. Bernal, G. Colon, M. Daturi, J.C. Lavalley, Catalysis Today, 59, 373 (2000). 

FIGURE 1.2 Composition dependence of conductivity for yttria-stabilized zirconia (YSZ) measured at 1000°C [7], yttria-doped bismuth oxide (YDB) at 600°C [6], and yttria-doped ceria (YDC) at 700°C [8],... 

Nguyen TL, Kobayashi K, Honda T, Iimura Y, Kato K, Neghisi, A et al. Preparation and evaluation of doped ceria interlayer on supported stabilized zirconia electrolyte SOFCs by wet ceramic processes. Solid State Ionics 2004 174 163-174. 

The activation energy for oxide ion conduction in the various zirconia-, thoria- and ceria-based materials is usually at least 0.8 eV. A significant fraction of this is due to the association of oxide vacancies and aliovalent dopants (ion trapping effects). Calculations have shown that the association enthalpy can be reduced and hence the conductivity optimised, when the ionic radius of the aliovalent substituting ion matches that of the host ion. A good example of this effect is seen in Gd-doped ceria in which Gd is the optimum size to substitute for Ce these materials are amongst the best oxide ion conductors. Fig. 2.11. 

A. Hartridge, A. Bhattacharya, Preparation and analysis of zirconia doped ceria nanocrystal dispersions, J. Nanoparticle Res. 1 (2001) 75-80. 

One of the exceptions was the discovery of high ionic conductivity in appropriately doped FaGa03.128 129 As in the other oxide ion conductors, its ionic conductivity depends on both the dopant level as well as on the nature of the dopant. A major difference to ceria and zirconia is the presence of two cations that can be substituted the detailed defect chemistry of such solid solutions is far from being fully understood. Co-doping of Sr on A sites and Mg on B-sites leads to an ionic conductivity of ca. 0.12—0.17 S cm 1 at 800°C,130-133 which is similar to doped ceria but considerably exceeds the value of YSZ (ca. 0.03 S cm 1 at 800°C80 81). The activation energy also varies with composition and can be as low as ca. 0.6 eV.130 131 At about 600-700°C, the... 

Ceria affords a number of important applications, such as catalysts in redox reactions (Kaspar et al., 1999, 2000 Trovarelli, 2002), electrode and electrolyte materials in fuel cells, optical films, polishing materials, and gas sensors. In order to improve the performance and/or stability of ceria materials, the doped materials, solid solutions and composites based on ceria are fabricated. For example, the ceria-zirconia solid solution is used in the three way catalyst, rare earth (such as Sm, Gd, or Y) doped ceria is used in solid state fuel cells, and ceria-noble metal or ceria-metal oxide composite catalysts are used for water-gas-shift (WGS) reaction and selective CO oxidation. 

Related systems It should be noted that specific properties for applications could be enhanced by using solid solutions, doped materials, and composites, instead of pure ceria. For example, ceria-zirconia solid solution is a well known ceria based material for enhanced OSC and high ionic conductivity for solid state fuel cell components. It is also used in the three way catalysts for automobile waste gas cleaning, because of the improved thermal stability, surface area, and reducibility. The synthesis, structure, and properties of ceria-zirconia have been actively studied for a long time. Di Monte and Kaspar et al. presented feature articles on the nanostructured ceria—zirconia-mixed oxides. The studies on phase, structures, as well as the microstructures are discussed and reviewed (Di Monte et al., 2004). 

S Atomistic simulation assisted synthesis and investigations The classical atomistic simulation techniques based on the pair potentials are suitable for the simulations of ceria nanoparticles even with a real sized model. Molecular d)mamics studies with several thousands of ions and up to hundreds of nanoseconds in a time scale have been carried out to interpret the diffusion, and crystal growth behaviors for pure and doped-ceria nanoparticles. Traditionally, the technique has been used to explore the oxygen ionic conductivity in ionic conductors such as ceria and zirconia (Maicaneanu et al., 2001 Sayle et al., 2006). 

Figure 12 Conductivities of selected oxides as a function of temperature. Doped ceria and zirconia, and lanthanum gallate are oxide ion conductors, while hariiun zirconate is a proton conductor (From S.M. Haile Materials for fuel cells. Materials Today 6 24-29 (March 2003)). (Reprinted from Ref. 148. 2003, with permission from Elsevier)...

Eguchi, K., Akasaka, N., Mitsuyasu, H., and Nonaka, Y., Process of solid state reaction between doped ceria and zirconia, Solid State Ionics, 2000, 135, 589-594. 

Zhou, X.D., Scarfino, B., and Anderson, H.U., Electrical conductivity and stability of Gd-doped ceria/Y-doped zirconia ceramics and thin films. Solid State Ionics, 2004, 175 19-22. 

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