Oxygen ion conductivity

The co-precipitation technique starts with an aqueous solution of nitrates, carbonates, chlorides, oxychlorides, etc., which is added to a pH-controlled solution of NH4OH, allowing the hydroxides to precipitate immediately. This method requires water-soluble precursors and insoluble hydroxides as a final product. The hydroxides are filtered and rinsed with water when chlorides are employed as starting materials and chlorine is not desired in the final product. After drying the filtrate, it is calcined and sintered. This method is being applied very successfully for oxygen-ion conducting zirconia ceramics [30],... 

E.C. Subbarao, and H.S. Maiti, Solid electrolytes with oxygen ion conduction, Solid State Ionics 11, 317-338 (1984). 

This presentation reports some studies on the materials and catalysis for solid oxide fuel cell (SOFC) in the author s laboratory and tries to offer some thoughts on related problems. The basic materials of SOFC are cathode, electrolyte, and anode materials, which are composed to form the membrane-electrode assembly, which then forms the unit cell for test. The cathode material is most important in the sense that most polarization is within the cathode layer. The electrolyte membrane should be as thin as possible and also posses as high an oxygen-ion conductivity as possible. The anode material should be able to deal with the carbon deposition problem especially when methane is used as the fuel. 

Yahiro, H. Eguchi, Y. Eguchi, K. Arai, H. 1988. Oxygen ion conductivity of the ceria samarium oxide system with fluorite structure. I. Appl. Electrochem. 18 527-531. 

Thus, measurement of the total conductivity together with the cell voltage allows the transport numbers of the ions to be determined (Fig. 8.17). The results show that at lower temperatures proton conductivity is of greatest importance, at middle temperatures oxygen ion conductivity becomes dominant, and at high temperatures the material is predominantly a hole conductor. Between these temperatures, at approximately 350°C the solid is a mixed H+ and O2- conductor while at approximately 650°C it is a mixed hole and O2- conductor. 

Shown in Figure 1.1 is the oxygen ion conductivity of selected oxides. Among these oxides, only a few materials have been developed as SOFC electrolytes due to numerous requirements of the electrolyte components. These requirements include fast ionic transport, negligible electronic conduction, and thermodynamic stability over a wide range of temperature and oxygen partial pressure. In addition, they must... 

Pure stoichiometric ceria is not a good oxygen ion conductor. The oxygen ion conductivity can be introduced dramatically by low valance doping. Thus the conductivity depends on the characteristics of the dopant elements and their concentrations. 

As shown in Equation (1.3), the oxygen ion conductivity of doped ceria is a function of both dopant concentration and temperature. At a given concentration, the conductivity is usually represented by the equation ... 

Due to its high oxygen ion conductivity, doped ceria has been considered as the electrolyte for SOFCs operated at low and intermediate temperatures since the 1990s. 

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