Redox Stability of SrNbxTi1-xO3-YSZ for Use in SOFC Anodes

The conductive properties of bulk SrNbxTi1-xO3 (SNT) and porous SrNbxTi1-xO3-yttria-stabilized zirconia (YSZ) composites for x=0.01, 0.05, and 0.20 have been examined under relevant solid oxide fuel cell (SOFC) operating temperatures and redox cycling conditions. The porous composite conductivities were approximately 1 order of magnitude lower than the corresponding bulk material. In order to obtain reasonable conductivity levels for SOFCs, samples were prereduced at 1400 degrees C in H-2. The conductivity of prereduced samples increased with increasing Nb content when directly measured in humidified H-2; however, when considering the conductivities measured after redox cycling, there appears to be no benefit to using higher dopant levels. After redox cycling at 800 degrees C, a composite conductivity of 1 S/cm at 800 degrees C in humidified H-2 (3% H2O) was achieved for x=0.01 and 0.05 and a composite conductivity of 0.5 S/cm was achieved for x=0.20. Fuel cell power densities of 415 mW/cm(2) at 700 degrees C and 640 mW/cm(2) at 800 degrees C were achieved in humidified H-2 (3% H2O) with a porous SNT-YSZ anode infiltrated with 1 wt % Pd and 3 wt % CeO2, a 50 mu m thick YSZ electrolyte, and an La0.8Sr0.2FeO3 (LSF), LSF-YSZ cathode. The implications of these results for the development of redox-stable anodes are discussed.