Zirconia-based Ceramic Electrolytes

The transmission electron microscopy was used to study the initial stage of the formation of the films of zirconia-based solid electrolytes, which were prepared by ion plasma sputtering on a glass-ceramic substrate having a thin ( 10 nm) layer of amorphous carbon. 

J. Xue, and R. Dieckmann. Oxygen partial pressure dependence of the oxygen content of zirconia-based electrolytes in Ionic and Mixed Conducting Ceramics Second International Symposium 94-12, 191-208 (1994) ES Meeting San Francisco, California. 

Other oxygen ion conductors that have potential use as solid electrolytes in electrochemical devices are stabilized bismuth and cerium oxides and oxide compounds with the perovskite and pyrochlore crystal structures. The ionic conductivity and related properties of these compounds in comparison with those of the standard yttria-stabilized zirconia (YSZ) electrolyte are briefly described in this section. Many of the powder preparation and ceramic fabrication techniques described above for zirconia-based electrolytes can be adapted to these alternative conductors and are not discussed further. 

The ceramic electrolyte is based on zirconia (Zr02) or ceria (Ce02), each of which is an electronic insulator but is conductive towards oxide ions (0 ) at high temperatures. This conductivity is achieved by doping the chosen oxide with ions of lower valency. For instance, when zirconia is doped with yttrium ions (Y ), oxide ion vacancies are formed in the parent lattice to compensate for the charge difference, i.e.,... 

Concerning non-porous membranes, these are categorized as dense ceramic electrolytes such as yttria-stabilized zirconia (YSZ) and perovskite membranes [16], which allow only the permeation of ionic oxygen. Permeation through metal membranes such as palladium and a palladium alloy is based on the selective dissolution of hydrogen and diffusion through the metal membrane. 

The solid oxide fuel cell (SOFC) is based on a thin layer of solid ceramic electrolyte of yttria-stabilized zirconia operating at 600 to 1000°C, which transfers the oxygen ion (O ) from the cathode to the anode. The high temperature is necessary to achieve sufficient ionic conductivity [14]. The electrochemical reaction in an SOFC can be expressed as equation (1.16) to equation (1.18). 

However, the state-of-the-art ceramic electrolyte material used in SOFC is the YSZ because YSZ has the highest oxide ion conductivity, lowest electronic conductivity, and lowest gas permeability to prevent gas crossover losses. The base material in the YSZ is the zirconia (Zr02), which is doped with yttria the dopant element to create oxygen vacancy sites and... 

On the basis of the model described above, one would expect that the enhancement of the transport properties should depend upon the degree of acidity of the ceramic s surface states. This is indeed the case as demonstrated by the behaviour of PEO-based polymer electrolytes using ceramic fillers with a high surface acidity, e.g. the sulfate-promoted superacid zirconia, S-ZrOi. The results show that this ceramic filler considerably enhances the transport properties of the electrolyte. 

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