Physical characterization of Y₂O₃–CeO₂–TiO₂ (YCT) mixed oxides and Ni/YCT cermets as anodes in solid oxide fuel cells

Mixed oxides in the binary Y₂O₃–CeO₂ (YC) and ternary Y₂O₃–CeO₂–TiO₂ (YCT) systems as well as the corresponding Ni cermets were evaluated in terms of application as anodes in solid oxide fuel cells (SOFCs) between 650 and 900 °C. X-ray diffraction (XRD) analysis of the YCT powders calcined up to 1,400 °C showed the cubic fluorite structure of YC and also the formation of an additional phase with pyrochlore structure. The thermal expansion of the ceramics measured in air and Ar/4% H₂ showed no significant differences in the temperature range of 25–800 °C. The absolute values of the total electrical conductivity of the ceramics measured between 450 and 900 °C in Ar/4% H₂ increased by about 1–2 orders of magnitude compared to those measured in air. Ni/Y_0.20Ce_0.80O_1.9 and Ni/Y_0.20C_0.75Ti_0.05O_1.9 cermets with 40 vol% Ni exhibited improved long-term stability regarding their electrical conductivity after annealing at 1,000 °C. The diffusion coefficient of Ce in the 8YSZ electrolyte was measured by compatibility tests. Electrochemical measurements on single SOFCs showed high polarization resistance at the anode/electrolyte interface.