Effect of Sm and Fe Co-Doping on Structural and Electrical Properties of CeO2 Solid Electrolyte

Abstract

High efficiency and environmental-benign characteristics of solid oxide fuel cell (SOFC) as an energy source have been receiving enormous attention to overcome global warming, pollution and fuel availability issues. Intensive research in SOFC focuses on developing cells that have high electrochemical performances and durability. The solid electrolyte that is commonly studied as a candidate for SOFC is samarium doped ceria (SDC) because it has higher oxygen ionic conductivity compared to yttria stabilized zirconia (YSZ). In this project, compositional modification of cerium oxide (CeO2) by single and double substitution of samarium oxide (Sm2O3) and iron oxide (Fe2O3) with composition of Ce0.8Sm0.2O1.9, Ce0.8Sm0.1Fe0.1O1.9 and Ce0.7Fe0.1Sm0.2O1.85 were studied. Samples were synthesized via conventional solid state reaction method by mixing the raw materials which is cerium oxide (CeO2), samarium oxide (Sm2O3) and iron oxide (Fe2O3), then pressed into pellet, and finally sintered in the range of 1400 oC to 1500 oC. X-ray diffraction (XRD) analysis for phase confirmation and impedance measurement for electrical conductivity were used in order to investigate the influences of the double dopants on the crystal structure and electrical properties. Optimum sintering temperature for sample in this study is 1480 oC. However, at this temperature, single phase was not obtained for Ce0.7Sm0.2Fe0.1O1.85 so this sample required different sintering profile. Ce0.8Sm0.2O1.9 and Ce0.8Sm0.1Fe0.1O1.9 samples show relative density above 97%. Ce0.7Sm0.2Fe0.1O1.85 sample shows highest conductivity, which is 0.613 Ω-1m-1 at 600 oC, followed by Ce0.8Sm0.2O1.9 (0.350 Ω-1m-1) then Ce0.8Sm0.1Fe0.1O1.9 (0.180 Ω-1m-1). Ce0.8Sm0.1Fe0.1O1.9 sample has highest activation energy compared to Ce0.8Sm0.1O1.9 and Ce0.7Sm0.2Fe0.1O1.85 which is 1.255 eV, while Ce0.8Sm0.2O1.9 is 0.828 eV and the lowest activation energy is Ce0.7Sm0.2Fe0.1O1.85 sample with 0.671 eV.