Electrochemical properties of nanocrystalline y_2-xPr _xRu₂O₇ pyrochlore for electrodic application in IT-SOFCS

Nanocrystalline powders of Y_2-xPr_xRu ₂O₇ were prepared by a co-precipitation method, and tested as an electrode on ESB and GDC electrolytes by electrochemical impedance spectroscopy in the temperature range of 300-750°C. The electrode polarization was studied as a function of praseodymium concentration in the cathode material. Both systems, Y_2-xPr_xRu ₂O₇/ESB and Y_2-xPr_xRu ₂O₇/GDC, showed a similar variation of the electrode area specific resistance (ASR). Y_1.5Pr_0.5Ru₂O ₇ cathode material presented the best performance, with ASR value of 0.19 Ωcm² on ESB and 4.23 Ωcm² on GDC at 700°C. Furthermore, the change in ASR with the oxygen partial pressure suggested that the rate limiting step is the surface diffusion of the adsorbed oxygen at the electrode surface to the triple-phase boundary. Thus, the low value of resistivity of the Y_1.5Pr_0.5Ru₂O ₇ in contact with ESB resulted from a much lower charge transfer resistance compared to the Y_2-xPr_xRu₂O ₇/GDC system. Also a partial solid diffusion of the cations at the electrode/electrolyte interface of Y_2-xPr_xRu ₂O₇/ESB contributed to lower the interfacial polarization. This suggested that Y_2-xPr_xRu₂O₇ is a promising material for cathode application in ESB-based electrolyte for intermediate temperature solid oxide fuel cells.