Ceria electrolytes conductivity

Most of the literature focuses on the aspects of sinterability and microstructure, but limited data on the electrical properties is available. Tok [152] reported a conductivity of 18.3 x 10-3 Scm-1 at 600°C for Gd0 jCeo.gOj 95, and we measured a high conductivity of 22 x 10-3 scm-1 for Sm0 2Cc08O 9 at the same temperature. Their activation energies are relatively low—less than 0.7 eV. Although conductivity data reported for doped ceria prepared with carbonate precipitation is varied from different authors [153-155], the conductivity is generally high and the activation energy is usually low for ceria electrolytes fabricated with this method. 

To introduce a barrier layer when utilizing doped ceria electrolytes (SDC, GDC, or lanthanum-doped ceria, LDC) to prevent the reduction of Ce4+ to Ce3+. Reduction of cerium cations results in unwanted electronic conductivity that lowers fuel efficiency [34], and mechanical degradation that results from the volume expansion of cerium ions upon reduction [35],... 

A possible explanation for the sharp increase in conductivity of the ceria electrolytes that occurs in contact with the proton-conducting alkali-metal carbonates or with nonconducting oxides was offered in a paper by Zhu et al. (2003). Adsorption of an excess number of oxygen ions (0 ) is possible at the contact surface areas between the nanoparticles of the two phases. In this way a new, additional interfacial conduction pathway is opened up for the ionic current. 

Similar views concerning the mechanism of conductivity enhancement in ceria electrolytes were expressed in a paper by Huang et al. (2005), where it was pointed out the interaction between the flows of negative oxygen ions and positive protons directed in opposite directions. 

A similar two-phase electrolyte which in addition to the ceria electrolyte contained powdered nickel-aluminum alloy to which NaOH had been added was suggested by Hu et al. (2006). This electrolyte had the distinguishing feature of being solid at room temperature but had a liquid phase that appeared in it at working temperatures of the fuel cell above 318°C. In this case again, mixed conduction by and H+ appears in the solid phase, and by Na" " and OH in the liquid phase. 

The ionic conductivity of ceria electrolyte is also expressed by relations given by Equations 7.48 and 7.49. 

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