Suitability of Sm 3+ - Substituted SrTiO 3 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, Sm x Sr 1−x TiO 3−δ (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 SrTiO 3 is x < 0.15. The X-ray Rietveld refinement for all samples indicated the perovskite cubic structure with a P m 3 ¯ m 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 Sm x Sr 1−x TiO 3 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 °C and scaled with the help of the Ghosh and Summerfield scaling model taking ν H and σ 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 Sm 0.10 Sr 0.90 TiO 3 sample was found to be 2.7 × 10 −1 S∙cm −1 at 650 °C, which is the highest among the other compositions. Hence, the composition Sm 0.10 Sr 0.90 TiO 3 can be considered as a promising material for the application as the anode in SOFCs.