Abstract

We have designed and synthesized by wet chemical techniques a family of excellent cathode materials to be used in intermediate-temperature solid-oxide fuel cell (IT-SOFC) devices based on SrCoO3-delta oxide. We have replaced Co by 10 and 15% of Ir4+ in SrCo1-xIrxO3-delta (x = 0.10 and 0.15), eluding the unwanted hexagonal phase of SrCoO3-delta by the introduction of a highly charged ion at the Co position. In this way, the ionic and the electronic conductivity, together with the catalytic activity for O-2 reduction, was substantially improved. After identification from X-ray diffraction, an in situ neutron powder diffraction study enabled the structural characterization between 25 and 800 degrees C, unveiling a tetragonal to cubic phase transition around 380 degrees C. A significant quantity of oxygen vacancies at 800 degrees C was identified, also characterized by thermogravimetric analysis. The thermal expansion is virtually linear, without abrupt changes except a subtle change of slope at 380 degrees C concomitant with the tetragonal-to-cubic order-disorder transition. A good chemical compatibility with the LSGM electrolyte is also shown. Electrical conductivity shows a metallic behavior in the 400-850 degrees C region, and impedance spectroscopy measurements yield polarization resistances as low as 0.07 Omega cm(2). Finally, in situ tests of the performance on electrolyte-supported single cells gave a power density of 891 mW/cm(2) at 850 degrees C, using pure H-2 as fuel, demonstrating that these materials perform as excellent cathodes for IT-SOFCs.