Low Temperature Densification and Electrical Property of a Carbonate-Added Proton Conducting Ceramic

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Proton conducting yttrium-doped barium zirconate (BZY) is one of the most studied materials for SOFC applications due to its high bulk proton conductivity, good chemical stability under CO2 and mechanical robustness. However, it requires a very high temperature (1700-2100°C) and long sintering time (>24 h), even with nano-sized powers, to sinter into a dense ceramic. In this paper, we demonstrate a unique approach to make a dense BZY at much lower temperatures. The method involves prefabrication of a porous BZY matrix by solid-state reaction from micro-sized powders of BaCO3, ZrO2 and Y2O3 and densification by impregnating the porous BZY matrix with a carbonate eutectic mixture (e. g., 62 mol% Li2CO3 and 38 mol% K2CO3) at 600oC. Thus fabricated solid-oxide and carbonate composite is also expected to be a mixed proton and carbonate-ion conductor (MPCC). The initial results show that there are no chemical reactions between BZY and carbonate. The microstructure of the composite MPCC is dense with the carbonate phase filling out the pores in the BZY matrix. The measured effective ionic conductivity reaches 0.33 and 0.38 S/cm at 600°C in wet air and in wet H2, respectively. The performance of a MPCC-based fuel cell is, however, severely limited by the electrode (Ag) resistance, which is expected to be improved with better electrode materials in future study.