Synthesis, structure and electrical properties of Mo-doped CeO ₂-Materials for SOFCs

In this paper, we report the synthesis, structure and electrical conductivity of Mo-doped compounds with a nominal chemical formula of Ce ^1-xMo_xO_2+δ (x = 0.05, 0.07, 0.1) (CMO). The formation of fluorite-like structure with a small amount of Ce ₈Mo₁₂O₄₉ impurity (JCPDS Card No. 31-0330) was confirmed using a powder X-ray diffraction (PXRD). The fluoride-type structure was retained under wet H₂ and CH₄ atmospheres at 700 and 800 °C, while diffraction peaks due to metal Mo were observed in dry H ₂ under the same condition. AC impedance measurements showed that the total conductivity increases with increasing Mo content in CMO, and among the investigated samples, Ce_0.9Mo_0.1O_2+δ exhibited the highest electrical conductivity with a value of 2.8 × 10^-4 and 5.08 × 10^-2 S cm^-1 at 550 °C in air and wet H₂, respectively. The electrical conductivity was found to be nearly the same, especially at high temperatures, in air, O ₂ and N₂. Chemical compatibility of Ce _0.9Mo_0.1O_2+δ with 10 mol-% Y ₂O₃ stabilised ZrO₂ (YSZ) and Ce _0.9Gd_0.1O_1.95 (CGO) oxide ion electrolytes in wet H₂ was evaluated at 800-1,000 °C, using PXRD and EDX analyses. PXRD showed that CMO was found to react with YSZ electrolyte at 1,000 °C. The area specific polarisation resistance (ASPR) of Ce _0.9Mo_0.1O^2+δ on YSZ was found to be 8.58 ohm cm² at 800 °C inwet H₂.