Direct synthesis of Ce0.8Sm0.2−xZnxO2−δ electrolyte by sol–gel for IT-SOFC

In this paper, high-quality nanosized Ce0.8Sm0.2−xZnxO2−δ (x = 0, 0.02, 0.04, 0.08, and 0.16) powders are successfully synthesized by sol–gel process for intermediate-temperature solid oxide fuel cell (IT-SOFC) application. The thermal behavior, porosity, crystal phase, surface microstructure, and electrical properties of Ce0.8Sm0.2−xZnxO2−δ are studied by thermogravimetric-differential scanning calorimeter (TG-DSC), Archimedes drainage method, X-ray diffraction (XRD), scanning electron microscope (SEM), and electrochemical impedance spectroscopy (EIS), respectively. The results show that Ce0.8Sm0.2−xZnxO2−δ electrolyte appears very high sintering activity even at sintering temperature as low as 1300 °C. The crystal phase of sample powders after sintered at 600 °C belongs to single-phase cubic fluorite structure with mean particle size of 15 nm. The lattice parameter increases first until doping 2 mol.% Zn and then decreases with more doping amount. Electrochemical performance results demonstrate that doping with appropriate amount of Zn can significantly improve the conductivity of SDC materials. The highest conductivity of 0.057 S·cm−1 at 800 °C is obtained for Ce0.8Sm0.16Zn0.04O2−δ, owing to high density, ultrafine grains, and increased grain boundaries. Furthermore, the fuel cell performance of Ce0.8Sm0.16Zn0.04O2−δ electrolyte is measured with 5 wt.% Fe-loaded activated carbon as the fuel. It delivers an outstanding performance, with an OCV of 1.02 V, a maximum power output of 408 mW·cm−2 at 850 °C, indicating that Ce0.8Sm0.16Zn0.04O2−δ may have potential application for IT-SOFC electrolyte materials.