Fabrication And Properties Of Zirconate/Salt Composite Proton Conductors

Protonic conductor of Y-doped zirconates exhibits good chemical stability and high bulk conductivity. However, its low total conductivity and high sintering temperature remain the main obstacles in its high-drain applications as electrolytes of solid state fuel cells (SOFC). This work deals with composites of high-temperature proton conductors BaZr_0.9Y_0.1O_2.5 (BZY10) and inorganic compounds such as sulphates and chlorides. The first step is to decrease the sintering temperature of BZY10. Furthermore, heterogeneous composites were fabricated with BZY10 as matrix and some inorganic salts as dispersant.The sintering temperature of BZY10 prepared by conventional solid-state reaction is very high. It is found that B₂O₃ is an effective sintering aid for zirconates. The sintering behavior and the DC electrical conductivity of BZY10 sample with 0.75wt % B₂O₃ sintered at 1500℃for 6h are as good as those of undoped BZY10. The overdoped B₂O₃(> 0.75 wt%)remained in the samples and formed a secondary phase that has a positive effect on sintering behavior but a negative effect on DC electrical conductivity of BZY10.The powders of BZY10 with high specific surface areas are synthesized by a glycine-nitrate combustion synthesis process. With the use of 0.75 wt% B2O3 as a sintering aid, the BZY10 proton conductor could be almost fully densified at 1400℃for 6h. The DC electrical conductivity is as high as that of the same system prepared by solid-state reaction.Three kinds of barium zirconate/salt composites are succesefully fabricated at the sintering condition of 1350℃/4h. The electrical conductivity of BZY10/K₂SO₄ reached 4.5×10^-4 S/cm at 700℃. Two preparation methods of BZY10/K₂SO₄ are studied. The sintering behavior and the DC electrical conductivity of BZY10/K2SO4 prepared by coating are better than those by ball milling.