Surface ionic conductivity, ceramic material

Silicate apatites present several limitations for their potential use as SOFC electrolyte. One of the main drawbacks of apatite-type materials resides in the difficulty in preparing dense ceramic materials, which are needed for SOFC operation. On the other hand, degradation of the ionic transport properties with time in reducing atmospheres at high temperatures has been reported for these materials, which was ascribed to silica migration and volatilisation in the ceramic surface (Yaremchenko et al, 2004).The apatite structure allows a large number of cation substitutions. Among them, the partial substitution of Sb+ by AP+ seems to enhance the ionic conductivity and partially suppress silicon volatilisation (Shaula et a/., 2005,2006). 

Kumar et al. [36] recently published a report on solid-state lithium-air batteries. The lithium-ion, conductive solid electrolyte membrane is based on glass-ceramic (GC) and polymer-ceramic materials. This solid electrolyte is used as the ionic conductive membrane between the lithium electrode and the air electrode. It also is used in the soHd composite air cathode prepared from high-surface-area carbon. The cell exhibited excellent thermal stabihty in the 30-105 °C temperature range... 

The last but not the least approach is addition of ceramic fillers. There is a variety of ceramic materials that offer relatively high ionic conductivities at room temperature (Goodenough et al. 1976 Hong 1976 Hooper 1977 Kafalas and Hong 1978 Sebastian and Gopalakrishnan 2003), however, applying them directly as electrolytes in commercial cells for mobile applications is not possible because they are brittle, difficult to process, and they cannot provide contact with the entire surface of porous electrodes made of powders as easily as polymers and liquids can do. Thus the first approach was using the polymeric electrolytes as conductive binders for the ceramic ionic conductors added to the polymer in a form of powder. Then inert materials were used. This will be described in detail in the next section. 

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