Use in Solid Oxide Cells and Oxygen Membranes

CERIA AND ITS USE IN SOLID OXIDE CELLS AND OXYGEN MEMBRANES 

Christodoulos Chatzichristodoulou, Peter T. Blennow, Martin S0gaard, Peter V. Hendriksen, and Mogens B. Mogensen 

Technical University of Denmark, Frederiksborgvej 399, DK-4000 Roskilde, Denmark 

The solid oxide fuel cell (SOFC) has been under development over several decades since it was invented by Baur and Preis in 1937. In order to commercialize this high temperature (600-1000 °G) fuel cell it was necessary to reduce the costs of fabricadon and operadon. Ceria-based materials are of potendal interest as both pure and doped ceria may help to decrease the internal electrical resistance of an SOFC by reducing the ohmic resistance of the electrolyte as well as the polarizadon resistance of both the fuel and the air electrode. Furthermore, the possibility of less fuel pre-treatment and having a lower water (steam) content in the natural gas fuel intended for the SOFC, due to the lower suscepdbility towards coke formation of ceria-containing fuel electrodes, may simplify the fuel cell system. Finally, ceria-based anodes seem less sensidve to poisoning by fuel impurities such as sulfur. The same type of cell has been developed for electrolysis and then called a solid oxide electrolysis cell (SOEC). As it is basically the same cell in both applicadons, it is often referred to as a solid oxide cell (SOC). It is anticipated that 

Many of the properties of ceria are intimately related to the tolerance of the fluorite structure towards high concentrations of oxide ion vacancies. In order to select the most appropriate doped ceria composition for a specific application, it is necessary to know the defect chemistry and thermochemistry of doped ceria and its relation to the thermomechanical, crystallographic, and transport properties. A brief description of the defect chemistry of ceria is provided in Section 12.2 of this chapter, followed by a short presentation of its thermal, crystallographic, and chemical properties and their dependence on doping and reduction. Thermodynamic data on X (in CeOg- ) as a function of oxygen partial pressure pOg and temperature, as well as the effect of substituents and particle size, will be a central topic of this chapter and will be discussed in Section 12.3. 

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Ceria and its Use in Solid Oxide Cells and Oxygen Membranes... 

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