Suitability of Sm3+-Substituted SrTiO3 as Anode Materials for Solid Oxide Fuel Cells: A Correlation between Structural and Electrical Properties

Perovskite anodes, nowadays, are used in any solid oxide fuel cell (SOFC) instead of conventional nickel/yttria-stabilized zirconia (Ni/YSZ) anodes due to their better redox and electrochemical stability. A few compositions of samarium-substituted strontium titanate perovskite, SmxSr1-xTiO3-delta (x = 0.00, 0.05, 0.10, 0.15, and 0.20), were synthesized via the citrate-nitrate auto-combustion route. The XRD patterns of these compositions confirm that the solid solubility limit of Sm in SrTiO3 is x < 0.15. The X-ray Rietveld refinement for all samples indicated the perovskite cubic structure with a Pm3m space group at room temperature. The EDX mapping of the field emission scanning electron microscope (FESEM) micrographs of all compositions depicted a lower oxygen content in the specimens respect to the nominal value. This lower oxygen content in the samples were also confirmed via XPS study. The grain sizes of SmxSr1-xTiO3 samples were found to increase up to x = 0.10 and it decreases for the composition with x > 0.10. The AC conductivity spectra were fitted by Jonscher's power law in the temperature range of 500-700 degrees C and scaled with the help of the Ghosh and Summerfield scaling model taking nu(H) and sigma(dc) T as the scaling parameters. The scaling behaviour of the samples showed that the conduction mechanism depends on temperature at higher frequencies. Further, a study of the conduction mechanism unveiled that small polaron hopping occurred with the formation of electrons. The electrical conductivity, in the H-2 atmosphere, of the Sm0.10Sr0.90TiO3 sample was found to be 2.7 x 10(-1) S.cm(-1) at 650 degrees C, which is the highest among the other compositions. Hence, the composition Sm0.10Sr0.90TiO3 can be considered as a promising material for the application as the anode in SOFCs.