Bulk Properties of the Oxygen Reduction Catalyst SrCo0.9Nb0.1O3-δ

The perovskite SrCo0.9Nb0.1O3-delta (SCN) has excellent electrochemical activity toward oxygen reduction, and it is also valuable as a possible model material for other state-of-the-art perovskite catalysts based on strontium and cobalt, such as Ba0.5Sr0.5Co0.8Fe0.2O3-delta (BSCF). Here we report thermogravimetric, conductivity, and diffraction measurements from SCN. We find that the thermodynamic stability limits of SCN are slightly more favorable than those reported for BSCF, although both materials exhibit a slow oxidative partial decomposition under likely operating conditions. In SCN, this decomposition is thermodynamically preferred when the average formal oxidation state of cobalt is greater than similar to 3.0+, but due to sluggish kinetics, metastable SCN with higher cobalt valence can be observed. The oxygen stoichiometry 3-delta varies from 2.45 to 2.70 under the conditions studied, 500-1000 degrees C and 10(-4)-1 bar O-2, which encompass both stable and metastable behavior. The electronic conductivity is p-type and thermally activated, with a value at 600 degrees C in air of 250 S cm(-1), comparable to that of La0.8Sr0.2MnO3-delta. The polaron migration enthalpy decreases linearly from 0.30 to 0.05 eV as 3-delta increases from 2.52 to 2.64. Thermal and chemical expansivities are also reported.