Mixed conducting oxides Y_xZr_1−x−yTi_yO_2−x/2 (YZT) and corresponding Ni/YZT cermets as anode materials in an SOFC

The physical properties of mixed-conducting oxides in the ternary system Y₂O₃–ZrO₂–TiO₂ with the general formula Y_xZr_1−x−yTi_yO_2−x/2 (YZT, where 0.133 < x < 0.25 and 0 < y < 0.15) are presented and evaluated in terms of an application as anode materials in solid oxide fuel cells (SOFCs). The total electrical conductivity of the ceramics with cubic fluorite structure in air mainly depends on the Ti content and decreases at 900 °C by about one order of magnitude from y = 0 to y = 0.15. Comparing the conductivity of contributions at 900 °C in Ar/4% H₂ the highest contributions of electronic conductivity were obtained for y = 0.15. For the Ni/YZT cermets, the enhanced adherence at the metal/ceramic interface, compared to Ni/8YSZ (8 mol% yttria stabilised zirconia), results in a better long-term stability in terms of electrical conductivity and microstructure after 1,000 h of annealing at 1,000 °C in reducing atmosphere. The electrochemical performance, tested in fuel cells with Ni/8YSZ, Ni/Y_0.20Zr_0.75Ti_0.05O_1.9 and Ni/Y_0.20Zr_0.70Ti_0.10O_1.9 anodes, decreased for Ni/Y_0.20Zr_0.70Ti_0.10O_1.9 under steam reforming conditions, most likely due to the reduced ionic conductivity of this specific YZT ceramic.