Phase-Assisted Tailored Conductivity of Doped Ceria Electrolytes to Boost SOFC Performance

Efforts to lower the operating temperature of solid oxidefuelcells include producing electrolytes that are sufficiently conductiveand stable below 600 & DEG;C. Doped ceria is one such electrolytebeing considered. During this study, codoped ceria powders (Ce0.8Sm0.2-x M (x) O2-& delta;, M = Bi3+, Zn2+ and x = 0, 0.05, 0.1, 0.15, 0.2)were prepared via coprecipitation by the addition of sodium carbonateand annealed at 800 and 1200 & DEG;C, respectively. Poor solubilityof the codopants in the ceria was observed for samples annealed at800 & DEG;C, resulting in a mixed-phase product including stable phasesof the oxides of these codopants. A second-stage partial incorporationof these codopants into the ceria lattice was observed when the annealingtemperature was increased to 1200 & DEG;C, with both codopants formingcubic-type phases of their respective oxides. Materials were characterizedusing X-ray diffraction (XRD), Raman spectroscopy, and Fourier transforminfrared spectroscopy (FTIR), as well as scanning electron microscopy(SEM) for structural and morphological investigations. The oxide ionconductivity was evaluated using electrochemical impedance spectroscopybetween 550 and 750 & DEG;C. Fuel cell performance tests of selectedsamples (annealed at 1200 & DEG;C) showed remarkable improvement inpeak power densities when the test temperature was increased from500 to 600 & DEG;C (& SIM;720 mW/cm(2) for Ce0.8Sm0.15Bi0.05O2-& delta; and & SIM;1230 mW/cm(2) for Ce0.8Sm0.15Zn0.05O2-& delta;), indicating possiblecontribution from the distinct cubic-type oxide phases of the codopantsin performance enhancement.