Strontium oxide thermal conductivity

The cathode materials used have to conduct both oxide ions and electrons satisfactorily, but, in addition, for compatibility, they must have similar thermal expansion coefficients as the electrolyte. The strontium-doped perovskite, LSM (see Section 5.4.2), is one of the materials of choice. 

The perovskite lanthanum chromite (LaCr03) is one of the exceptional ceramic compounds that are chemically very resistant to both oxidizing and reducing ambients. Moreover, being an electronic conductor, it is eminently suitable as a bipolar connector in solid oxide fuel cells. It is evident that the thermal expansion coefficients of the different components in a fuel cell (electrolyte, electrodes, bipolar connector) must be closely matched. Doping the chromite with strontium or magnesium ions is necessary to increase its electronic conductivity as well as its sinter activity. 

We took advantage of the dispersibility of Pd Ce02 core-shell structures to deposit them into the porous scaffold of SOFC materials as anode catalysts in order to enhance the thermal stability of these materials. The porous scaffolds were composed of yttrium-stabilized zirconia (YSZ) covered with a film of the conductive oxide lanthanum strontium chromium manganite (LSCM). For comparison of the activity and thermal stability, we prepared other electrodes that were identical except that the catalyst was simply Pd (from Pd(II) nitrate) in one case and a mixture of Pd and CeOg (from Pd(II) and Ce(III) nitrate salts) in the other. All the samples were first calcined at 700 °G to remove any by-products and to stabilize the materials. Then, accelerated aging tests were performed by calcining the samples at 900 °C for 2 hours. Initially we tested all the formulations in symmetric cells, e.g. cells where the anode and cathode materials are the same. The corresponding Nyquist plots are shown in Fig. 7.12(a). 

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