Fundamentals of Synthesis, Sintering Issues, and Chemical Stability of BaZr_0.1Ce_0.7Y_0.1Yb_0.1O_3-δProton Conducting Electrolyte for SOFCs

Fundamentals of synthesis, sintering issues, and chemical stability of BaZr0.1Ce0.7Y0.1Yb0.1O3-δ (BZCYYb) proton conducting electrolyte material were studied. Solid state reaction (SSR) and glycine nitrate process (GNP) methods were used to synthesize BZCYYb powders. The GNP method produced powders with higher purity and smaller particle size in reduced heat-treatment time and temperature. It was found that BZCYYb material, despite its high proton conductivity, has surprisingly high tendency to react with common substrate materials including alumina, zirconia, and even ceria during high temperature sintering. This led to significant barium loss and even disintegration of the perovskite phase. In addition, during sintering, BZCYYb also lost Ba through gas phase. The barium loss and unwanted side reactions with substrates could be suppressed either using enclosure of a platinum substrate and a cover or protective layers of BZCYYb powders. On the other hand, using metal oxide sintering aids such as NiO helps reducing sintering time and temperature which mitigates the extent of unwanted reactions. Finally, isothermal exposure experiments showed that at 750°C, chemical stability limits for BZCYYb in CO2 and H2S contaminated atmospheres are below ∼50 vol. % of CO2 and between 50 and 100 ppm of H2S, respectively, and they shift to lower values for Ba-deficient BZCYYb.