Novel ruthenium pyrochlore materials for cathode application in intermediate temperature solid oxide fuel cells (IT-SOFCs)

The performance of solid oxide fuel cells, which operate in the temperature range of 500-700°C (IT-SOFCs), strongly depends on the cathode employed because the interfacial polarization increases rapidly with decreasing temperature. Pyrochlore oxides with Ru on the B-site of the crystal lattice have been shown to have excellent electro catalytic behaviour for oxygen reduction reaction and high electrical conductivity. These characteristics make pyrochlore ruthenates good candidates for IT-SOFCs cathodes.;In this work, several compositions of Y2-xPrxRu 2O7 (x = 0, 0.2, 0.5, 1, 1.5, 2) pyrochlore powders were prepared by a soft precipitation method. All the synthesized powders were single pyrochlore phase with particles size depending on the material compositions. Praseodymium (Pr) was introduced in the A-site with the intent to improve the material electrical proprieties and consequently the overall cathode performance. In fact, without destabilizing the pyrochlore structure, Pr caused structural changes that allow higher electron mobility. The electrical measurements showed that the electrical conductivity of the material increased with increasing the Pr content.;Compositions of Y2-xPrxRu2O7 were tested as a cathode to compare its electro-catalytic effect with either of two electrolytes, gadolinium doped ceria (GDC) or erbium stabilized bismuth oxide (ESB). Both systems, Y2-xPrxRu2O 7/ESB and Y2-xPrxRu2O7/GDC, showed a similar variation of the electrode area specific resistance (ASR) with Pr content. This trend was shown to be due to a change of the cathode microstructure upon increasing Pr content.;The 25 mol % Pr cathode material on ESB electrolyte presented the best performance. A change of ASR as a function of oxygen partial pressure suggested that the oxygen diffusion is the limiting step of the electrode kinetics. Hence, the better cathode performance on ESB resulted from a much lower charge transfer resistance compared to the GDC system. A partial solid diffusion observed using SEM on the Y1.5Pr0.5Ru2O 7/ESB interface likely contributed to lower the interfacial polarization in this system. These results suggested that the nanocrystalline powders of Y1.5Pr0.5Ru2O7 electrode are promising materials for cathode application in ESBbased electrolyte for intermediate temperature solid oxide fuel cells (IT-SOFCs).