Tailoring the Stability of Ti-Doped Sr2Fe1.4TixMo0.6−xO6−δ Electrode Materials for Solid Oxide Fuel Cells

Abstract

In this work, the stability of $Sr_{2}(FeMo)O_{6−δ}$-type perovskites was tailored by the substitution of Mo with Ti. Redox stable $Sr_{2}Fe_{1.4}Ti_{x}Mo_{0.6−x}O_{6−δ}$ (x = 0.1, 0.2 and 0.3) perovskites were successfully obtained and evaluated as potential electrode materials for SOFCs. The crystal structure as a function of temperature, microstructure, redox stability, and thermal expansion properties in reducing and oxidizing atmospheres, oxygen content change, and transport properties in air and reducing conditions, as well as chemical stability and compatibility towards typical electrolytes have been systematically studied. All $Sr_{2}Fe_{1.4}Ti_{x}Mo_{0.6−x}O_{6−δ}$ compounds exhibit a regular crystal structure with Pm-3m space group, showing excellent stability in oxidizing and reducing conditions. The increase of Ti-doping content in materials increases the thermal expansion coefficient (TEC), oxygen content change, and electrical conductivity in air, while it decreases the conductivity in reducing condition. All three materials are stable and compatible with studied electrolytes. Interestingly, redox stable $Sr_{2}Fe_{1.4}Ti_{0.1}Mo_{0.5}O_{6−δ}$, possessing 1 μm grain size, low TEC $(15.3 \ × \ 10^{−6} \ K^{−1})$, large oxygen content change of $0.72 \ mol·mol^{−1}$ between 30 and 900 °C, satisfactory conductivity of $4.1–7.3 \ S·cm^{−1}$ in $5% \ H_{2}$ at 600–800 °C, and good transport coefficients D and k, could be considered as a potential anode material for SOFCs, and are thus of great interest for further studies.