Total electrical conductivity and defect structure of ZrO2-CeO2-Y2O3-Gd2O3 solid solutions

The use of a bilayer composite YSZ-CGO (yttria-stabilized zirconia-gadolinia-doped ceria) electrolyte for intermediate-temperature solid-oxide fuel cells (SOFCs) is still problematic, due to solid-state reaction and interdiffusion phenomena occurring between YSZ and CGO. To overcome this problem, a gradation in the microstructure between the single materials is proposed. To optimize the composition of the interlayer with respect to conductivity, different compositions of the system CGO(x)YSZ(1-x) were prepared and characterized in order to study their transport properties. Conductivity was found to reach a minimum for solid solutions where Zr and Ce are present in equimolar quantities. The latter are, however, the most appropriate candidates to be applied as interlayers between the two single materials. Keeping the Ce/Zr atomic ratio approximately equal to one, different solid solutions were prepared and characterized by varying the concentration of the trivalent cations present, in order to clarify their role in the transport properties of the material. For one of the better conducting systems the cell performance of the composite YSZ-interlayer-CGO film electrolyte is simulated and compared to that of the YSZ-CGO film electrolyte. (C) 2000 Elsevier Science B.V. All rights reserved

5 mol% TiO2-doped Ni-YSZ anode cermets for solid oxide fuel cells

The influence of doping YSZ (8 mol% yttria stabilized zirconia) with 5 mol% TiO2 on the thermal expansion coefficient, electrical conductivity and microstructure was examined for different cermets as a function of Ni-content. Thermal expansion measurements showed that TiO2 contributes to the reduction of the thermal expansion coefficient values of the cermet material. The incorporation of TiO2 into the YSZ lattice was found to reduce slightly the ionic conductivity of the pure ceramic, while under reducing conditions the electronic contribution, due to the reduction of Ti+4 to Ti+3, results in a decrease of the activation energy for conduction in the order of 13%. For the TiO2-doped cermets the electrical conductivity was always better than that of the undoped, exhibiting a lower degradation rate at 1000 degreesC. Based on microstructure examination of the samples, this degradation was attributed to the lower agglomeration trend of the Ni-particles of the doped cermets compared to the Ni-YSZ cermet. (C) 2000 Elsevier Science B.V. All rights reserved