Acceptor-doped ceria exhibits mixed ionic electronic conduction in reducing conditions and chemical stability against sulfur poisoning and coking. This thesis’s primary goal is to explore new anode materials based on ceria–solid solutions for solid oxide fuel cells (SOFCs). The physicochemical and electrochemical performance of Ce0.9–xY0.1MnxO2–δ (x = 0 to 15 mol%) (CYMO) and Ce0.87Y0.1Mn0.01N0.02O2-δ (N = Mg or Ca) were studied. Among the materials investigated in this study, Ce0.89Y0.1Mn0.01Mg0.02O2–δ (Mg-CYMO) showed the highest total conductivity of 0.2 S cm−1 at 700 °C in H2. An area specific polarization resistance of 0.23 Ω cm2 was observed for both Mg-CYMO and Ce0.8Y0.1Mn0.1O2-δ (10CYMO) at 800 °C, in wet H2. Chronoamperometric measurement for the symmetrical cell configuration based on 10CYMO electrodes showed stable performance upon exposure to 10 ppm H2S/H2. In a full cell configuration, 10CYMO (anode)/YSZ (electrolyte)/La0.8Sr0.2MnO3 (LSM)-YSZ cathode, polarization resistance of 1.4 Ω cm2 and power density of 75 mW/cm2 were obtained at 800 °C in wet H2.
The main challenge of employing proton-conducting electrolytes in SOFC is their poor chemical stability in the presence of steam and hydrocarbon fuels. Another goal of this thesis is to develop a chemically stable proton-conducting electrolyte for SOFCs. The effects of Fe and Co substitution on the electrical and physicochemical properties of BaCe0.9Sm0.1O3–δ (BCS) were evaluated. Thermogravimetric analysis showed that incorporation of 5 to 10 mol% Fe or Co in BCS did not improve the chemical stability in CO2 at elevated temperatures. The BCSC10 sample sintering at 1400 °C showed the highest electrical conductivity of 0.02 S cm-1 at 600 °C in air, but it did not show any appreciable proton mobility under humidified atmosphere.