Zirconia area specific resistance

It is considered that the bulk area specific resistance i o must be lower than l o = k/<7 = 0.15 Qcm, where L is the electrolyte thickness and a is its total conductivity, predominantly ionic [39]. At present, fabrication technology allows the preparation of reliable supported structures with film thicknesses in the range 10-15 pm consequently, the electrolyte ionic conductivity must be higher than 10 Scm. As shown in Figure 12.9, a few electrolytes (ceria-based oxides, stabihzed zirconias, and doped gallates) exceed this minimum ionic conductivity above 500 °C. 

In order to improve the performance of SOFC, a thirmer yttria-stabilized zirconia (YSZ) electrolyte is considered for lower ohmic resistance and for operation in the intermediate temperature range of 500°C-800°C. Ionic conductivity decreases with decrease in temperature and hence the area-specific resistance (ASR) of an electrolyte increases with lower operating temperature. Fabricating the electrolyte in a dense and thinner film reduces the ASR or the resistance to ionic transport, allowing a lower operating temperature. For this purpose, efforts are being made in fabricating SOFC cell on the basis of either a thicker anode-supported or a thicker cathode-supported SOFC... 

Similar results were found by Bozo [44]. Palladium deposited onto ceria-zirconia Ceo67Zro3302 solid solution showed very high activity in methane combustion (T50 close to 300 C) but similar to that of palladium deposited onto alumina. Like for the case of platinum a deactivation is observed during tests at temperatures comprised between 200°C and 400 C (Fig. 13.3). However when aged at 1000 C under an air+water mixture this catalysts showed superior resistance compared to classical catalysts as far as activity is considered. Despite a severe sintering of both metal (dispersion is now 1%) and support, whose surface area is close to 4 mVg, T50 was shifted to 420 C, i.e. 120°C only, still much lower for platinum deposited on the same support which showed a TSO close to 620°C. Calculation of specific activities in the 200-300°C range have clearly evidenced that ceria-zirconia support does not have any influence upon performance of PdO in... 

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