Electrical, Chemical, and Electrochemical Properties of Double Perovskite Oxides Sr2Mg_(1-x)Ni_xMoO_(6-δ) as Anode Materials for Solid Oxide Fuel Cells

摘要

The suitability of double perovskite oxides of composition Sr2Mg_(1-x)Ni_xMoO_(6-δ) (SMNM, x - 0—0.9) as anode materials for solid oxide fuel cells (SOFCs) was evaluated. Single double perovskite structures could be obtained up to x - 0.9 in syntheses at ambient atmosphere. However, after reduction at 800 °C, trace amounts of impurities were detected in the sample with x = 0.9, suggesting that the upper limit for the Ni content (x) in SMNM is less than 0.9 under SOFC operating conditions. The electrical conductivity of SMNM increases with increasing Ni content because of the increase in the concentration of electronic defects, [Mo_(mo~(6+))~(5+)'], and the decreased band gap energy, as revealed by first-principles calculations. The substitution of Ni can facilitate the charge-transfer process of the electrode reaction, decrease the polarization resistance, and thus increase the power density of a single cell. X-ray photoelectron spectroscopy and temperature-programmed reduction measurements were used to explain the reason for the performance improvement. SMNM showed good chemical compatibility with Ce_(0.8)Sm_(0.2)O_(2-δ) (SDC) but a slight reactivity with the electrolyte La_(0.8)Sr_(0.2)Ga_(0.83)Mg_(0.17)O_(3-δ) (LSGM) at 1300 °C. The use of an SDC buffer layer could avoid the interface reaction between the SMNM anode and the LSGM electrolyte, resulting in better cell performance. The Sr2Mg_(0.3)Ni_(0.7)MoO_(6-δ) electrode exhibited a maximal power density of 160 mW cm~(-2) at 800 °C with an electrolyte (LSGM, 400 μm) -supported cell configuration.