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

Abstract

Fundamentals of synthesis, sintering issues, and chemical stability of BaZr 0.1 Ce 0.7 Y 0.1 Yb 0.1 O 3-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 CO 2 and H 2 S contaminated atmospheres are below ∼50 vol. % of CO 2 and between 50 and 100 ppm of H 2 S, respectively, and they shift to lower values for Ba-deficient BZCYYb.

Electrochemical Behaviors for Ag, LSCF and BSCF as Oxygen Electrodes for Proton Conducting IT-SOFC

“…[11][12][13][14][15] The stability and compatibility between BZCYYb and BSCF at intermediate temperature have been studied before. 11 In order to verify the chemical compatibility between LSCF and BZCYYb under cell fabrication condition, powders of the two materials with weight ratio of 7:3 were intimately mixed and exposed to ambient air at typical LSCF-BZCYYb cathode firing temperature of 1000…”

“…12 Then, ∼0.16 mm 2 cathodes were brush painted onto both sides of the sintered BZCYYb pellets with pure silver paste, LSCF paste, mixed LSCF-BZCYYb paste (LSCF: BZCYYb weight ratio of 7:3), and BSCF paste, respectively (Please refer to 11 for formulation of typical cathode pastes used). All painted samples were fully dried in an air oven at 100…”

Effects of H2O and CO2on Electrochemical Behaviors of BSCF Cathode for Proton Conducting IT-SOFC

“…[7][8][9] In comparison, proton conducting oxides, many of which are perovskite-structured, offer higher ionic conductivity with low electronic transport number as well as lower activation energy at intermediate temperature. [10][11][12][13][14][15][16] As a result, they are regarded as the preferred electrolyte for IT-SOFC. 17 For IT-SOFC, the cathode process is generally regarded as the rate-limiting step due to its high activation energy compared to the electrolyte.…”

Decomposition reaction of BaZr_0.1Ce_0.7Y_0.1Yb_0.1O_{3−δ} in carbon dioxide atmosphere with nickel sintering aid

“…Indeed, a significant phase decomposition of BZCYYb perovskite phase into BaCO 3 and CeO 2 phase in 50% CO 2 and 50% H 2 atmosphere at 750°C, which is higher than this study, was reported. 13) 3.2 Phase change of BZCYYb-Ni after exposure to CO 2 and H 2 -CO 2 atmosphere…”

“…9),12) However, other studies reported on its reactivity with carbon dioxide. 13), 14) Thus, the chemical stability of this BZCYYb proton conductor is still not clear. Furthermore, the effect of nickel sintering aid on chemical stability is also important because nickel is dissolved into the electrolyte in the case of anode-support-type cell.…”