Fabrication And Properties Of Bazro₃/baceo₃-based Composite Proton Conductors

Zirconate proton conductor had good chemical stability and high bulk conductivity; however, its total conductivity was low due to its large area and high resistance of the grain boundary, which limited its applications to SOFC or other devices. Methods of improving the sintering behavior and conductivity of zirconate materials were investigated in this work.First, the precursor Ba(Zr_0.9-xCe_x)Y_0.1O_3-δ (x=0.09, 0.18, 0.27) were synthesized by the conventional solid state reaction route. The sintering behavior and electrical conductivity showed that B-0.27 was the best among the three samples and was chosen for the next experiment. Secondly, impact of ZnO on sinterability was studied. ZnO was able to form a solid solution with B-0.27, resulting in the enhancement of sinterability. When the content of ZnO was 2 mol% (BZ-2), the sample had highest DC conductivity, reaching 9.27×10^-3 S/cm at 800℃in wet H2 atmosphere. The maximum power density was up to 12.4 mW/cm² with an electrolyte support configuration fuel cell. Finally, composite proton conductors doped by three different salts were prepared and researched. In BZ-2/NaOH multiphase system, NaOH could exist at grain boundaries in molten state. It could enhance the proton diffusion in the grain boundary, then the total proton conductivity increased to 10^-2 S/cm magnitude at 800℃. In BZ-2/Na₂CO₃ multiphase system, Na₂CO₃ decomposed after sintering, the amount of alkali metal oxides remained in the matrix was small. Further more, Na₂O had rather poor stability and could react with a variety of substances. So the salt did not play a role in improving proton conductivity. In BZ-2/CaF₂ multiphase system, CaF₂ could form an eutectic in the matrix, so the system could be densified at 1300℃. The conductivity of this system was mainly promoted by intrinsic defects. The concentration of defects was severely affected by temperature. As a result, the conductivity changed significantly with temperature. The activation energy of sample BZF-20 was up to 1.42eV.