Doped ceria reduction

Pure and doped ceria are mixed ionic and electronic conductors under reducing atmospheres, due to considerable p-type electronic conductivity under reducing conditions. The electronic conduction is due to the reduction of Cc4 to Ce3+ under... 

Bao 5Sr0 5Co08Fe0 2O3 (BSCF) shows extremely high electrochemical activity for the 02 reduction reaction at intermediate temperatures. Shao and Flaile [105] applied BSCF as cathode to a doped ceria electrolyte cell and achieved the power densities of... 

To introduce a barrier layer when utilizing doped ceria electrolytes (SDC, GDC, or lanthanum-doped ceria, LDC) to prevent the reduction of Ce4+ to Ce3+. Reduction of cerium cations results in unwanted electronic conductivity that lowers fuel efficiency [34], and mechanical degradation that results from the volume expansion of cerium ions upon reduction [35],... 

The intermediate- and low-temperature materials exhibit both significant oxygen ion and electron conductivity. This means that the oxygen reduction can take place everywhere in the cathode and is not restricted to the TPBs as in the LSM-type cathodes. An option for compensating the relatively low oxygen ion conductivity of LSC and LSCF at operating temperatures around 600 °C is by mixing the material with (doped) ceria [79, 80],... 

Finally, another possibility often discussed in the literature is that cation dopants from the electrode may enhance the electronic conductivity of the gas-exposed surface of the electrolyte in the vicinity of the TPB, thereby extending the reduction zone along the electrolyte surface via mixed conduction. The surface exchange rate of oxygen on both YSZ- and rare-earth-doped ceria (as measured by isotope methods) is only about 1 order of magnitude lower than on LSM at 700 Thus, if there were sufficient... 

Figure 4.16 a Schematic of a temperature-programmed analysis setup b TPR profile of CuO, CeOj, and a copper-doped ceria sample, Ceo.9Cuo.1O2, showing the effect of Cu doping on the reduction temperature. 

Furthermore, the electrode material must be reasonably stable and not change its volume as a result of reduction or oxidation because such a volume change may cause the electrode to peel off the electrolyte. Also, the thermal expansion coefficient (TEC) of the electrode material must be close to the electrolyte material. Thus, in order to select a proper composition of the doped ceria for a specific electrode application, it is necessary to have knowledge of the ceria chemistry and its relation to the thermal, crystallograhical and electrical properties of the doped ceria. Therefore, the next sections briefly describe the ceria chemistry and the related properties. 

Recently, it has been reported by Chiang et al/ that nanocrystalline (ca. lOnm crystallite size) undoped and doped ceria are very easily reduced. The heat of reduction was found to be less than one-half of the value for conventional polycrystallinc and single crystal samples. 

Table 15.1. Expansion on reduction of pure and gadolinia doped ceria ai lOOtTC. Sv.(>o Vegard s...

---