Electrical properties and redox stability of tantalum-doped strontium titanate for SOFC anodes

SrTaxTi1−xO3 (STT) with x = 0.01, 0.05, and 0.10, has been investigated as a potential electron conductor for solid oxide fuel cell (SOFC) anodes. STT was found to be chemically stable under oxidizing and reducing conditions and chemically compatible with yttria-stabilized zirconia (YSZ). The coefficient of thermal expansion (CTE) was near that of YSZ, ranging from 11.3 to 11.8 × 10−6 K−1. The conductive properties of bulk STT and porous STT–YSZ composites were studied under relevant SOFC operating temperatures and redox cycling conditions. In order to achieve reasonable conductivities, samples were initially reduced at 1673 K. Conductivity after redox cycling was higher for lower dopant concentrations. The redox stable conductivity of a porous composite with x = 0.01 was 1.1 S/cm at 1073 K in humidified H2 (3% H2O). Fuel cell tests indicated an anode impedance of 0.4 Ω cm2 at 973 K in humidified H2 for STT–YSZ anodes infiltrated with 3 wt.% CeO2 and 1 wt.% Pd.