Importance of Solid-Liquid Interface on Electrochemical Performance of Doped Ceria-Carbonate Composite Electrolyte for High Temperature Fuel Cells

Abstract

Samaria-doped ceria (SDC)/carbonate composite electrolytes were recently developed for high temperature fuel cell applications. Conventional LiAlO2 was replaced by SDC as the matrix phase and lithium/sodium carbonate was selected as the second phase. In this study, the porous SDC (Sm0.2Ce0.8O1.9; SDC) matrix was fabricated. Then, the molten lithium sodium carbonate ((Li0.52Na0.48)2CO3; LNC) is infiltrated to form a composite electrolyte.From the cell testing in this study, the SDC/LNC cell show higher power density (340mW/cm2) than LiAlO2/LNC cell (154mW/cm2) at 650°C. This result suggests that the SDC-LNC composite electrolyte may be a better electrolyte for high temperature applications. In addition, the effects of solid-liquid interface was investigated using matrix with various pore sizes ranging from 5 to 20 μm. When the pore size of structural matrix was changed from 20 to 5 μm, the power density measured increased from 126 to 340mW/cm2 at 650oC. This can be attributed to the small pores having higher interface area, and the increased interface area is effective for transportation of ions. In other words, the super-ionic conducting path may exist at this interface, where the defect concentrations are high.Through the results and calculations of the designed experiments, the importance of the interface is realized. Finally, it may be concluded that the interface was mainly contributed by oxygen ion conduction using DC measurement under the control of different atmospheres and TEM analysis. High-resolution SEM, XRD, and Electrochemical Impedance Spectroscopy were employed to conduct microstructural, structural and impedance analyses.