Thermomechanical, transport and anodic properties of perovskite-type (La_0.75Sr_0.25)_0.95Cr_{1鈭?span style='font-style: italic'>x}Fe_xO_{3鈭?span style='font-style: italic'>未}

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• 作者：M.F. Lü ; ^a ; E.V. Tsipis^b ; J.C. Waerenborgh^b ; A.A. Yaremchenko^a ; V.A. Kolotygin^a ; S. Bredikhin^c ; V.V. Kharton^a ; ^{kharton@ua.pt}
• 关键词：SOFC anode ; Lanthanum chromite&ndash ; ferrite ; Mixed conductivity ; Mö ; ssbauer spectroscopy ; Dilatometry ; Electrode polarization
• 刊名：Journal of Power Sources
• 出版年：2012
• 期刊代码：58_03787753
• 类别：ce
• 出版时间：15 May, 2012
• 卷：206
• 期：Complete
• 页码：59-69
• 文件大小：1090 K

摘要

Effects of iron doping on the functional properties of (La,Sr)CrO₃-based electrode materials have been appraised in a range of conditions relevant for SOFCs and other electrochemical applications. M枚ssbauer spectroscopy of perovskite-type (La_0.75Sr_0.25)_0.95Cr_1鈭?em>xFe_xO_3鈭?em>未 (x = 0.3-0.4), combined with thermogravimetry and X-ray diffraction, shows that the prevailing oxidation state of iron cations in both oxidizing and reducing atmospheres remains 3+. The redox behavior and transport properties are, therefore, essentially governed by Cr^3+/4+ couple, leading to dominant p-type electronic conduction in the oxygen partial pressure range from 0.5 down to 10^鈭?0 atm at 973-1223 K. The total conductivity and Seebeck coefficient variations indicate that the electronic transport decreases with iron additions as the hole concentration and mobility become lower. The partial ionic conductivity estimated from the steady-state oxygen permeability under air/H₂-H₂O-N₂ gradients is 0.05-0.08 S cm^鈭? at 1223 K and p(O₂) = 10^鈭?7 atm, and increases with x due to rising oxygen deficiency. A similar tendency was observed for chemical expansion studied by the controlled-atmosphere dilatometry, whereas the average thermal expansion coefficients are almost independent of x and vary from 11.1-11.3 脳 10^鈭? K^鈭? in air down to 10.3-10.5 脳 10^鈭? K^鈭? in CO-CO₂ at 350-1370 K. The electrochemical activity of porous (La_0.75Sr_0.25)_0.95Cr_0.7Fe_0.3O_3鈭?em>未 anodes with Ce_0.8Gd_0.2O_2鈭?em>未 interlayers, applied onto LaGaO₃-based solid electrolyte, is higher compared to (La_0.75Sr_0.25)_0.95Cr_0.5Mn_0.5O_3鈭?em>未 when no metallic current-collecting layers are used. Increasing iron content lowers the electrode performance in wet H₂-containing atmospheres, in correlation with electronic conduction.