Microcrystalline ceria

As with microcrystalline ceria, the doping of nanocrystalline Ce02 x with various cations (Zr, La, Y, Tb, Lu, etc.) has been shown to improve reducibility and to enhance thermal stability (by hindering crystallite growth). 

Another interesting consequence of the increased surface and grain-boundary density of nanocrystalline ceria is the enhanced solubility of dopants with a large size mismatch as they can be accommodated at the interfaces. The apparent solubility of copper in nanocrystalline CeOs.x was determined to be 10 mol%/ which is a significant enhancement relative to microcrystalline ceria, where a solubility limit of 1 mol% is expected (see Section 12.2.2.2). 

Figure 12.13 Temperature dependence of the electrical conductivity (total inplane except from 9b and lOa-d that are measured cross plane) under oxidizing conditions of Gd-doped ceria thin films reported in the literature. The total conductivity of microcrystalline Ceo.9Gdo.,0, 95 x is shown for comparison. (See Table 12.2 for a description of the materials.)...

Figure 12.14 Pq dependence of the electrical conductivity of Gd-doped ceria thin films and pellets at 600 °C and microcrystalline CeogGdo jOj gs. for comparison. The crystallite size and composition of the films are provided in the legend.

From the literature it is clear that nano-structured ceria has several advantages over similar microcrystalline materials. In SOFC applications, resistance to impurities such as sulfur, and resistance to carbon formation when hydrocarbons are used as fuel, have been reported. The high density of surface defects in nanostructured materials provides a large number of active sites for various surface interactions and surface exchange processes. There are clearly interesting features in nano-sized ceria compounds that need further exploration. The possibility of minimizing pretreatment and water vapor partial pressure in e.g. the natural gas feed due to lower susceptibility to coke formation of ceria containing fuel electrodes (anodes), may simplify the fuel cell system. 

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