Doped lanthanum cobaltite

Figure 8.15 Calculated composition versus oxygen stoichiometry curves for Lai- SrjCoCb-s. [The two experimental points are taken from data in A. N. Petrov, V. A. Cherepanov, and A. Y. Zuev, Thermodynamics, Defect Structure and Charge Transfer in Doped Lanthanum Cobaltites An Overview, J. Solid State Electrochem., 10, 517-537 (2006).]...

Single-phase perovskite MIECs such as Sr-doped lanthanum cobaltite (LSC), lanthanum ferrite (LSF), lanthanum cobalt ferrite (LSCF) and samarium cobaltite (SSC), and Ca-doped lanthanum ferrite (LCF) [13] are sometimes used alone in SOFC cathodes, as depicted in the lower right-hand comer of Figure 6.1, but combining an... 

The cathodes consist of manganites or cobaltites of lanthanum doped with divalent metal ions, for example, Lai (Srj(Mn03 (LSM) or Lax (Srj(Co03 (LSC), where 0.15 cathode materials also have some electronic conductivity that secures a uniform current distribution over the entire electrode. The doped lanthanum cobaltite has a higher ionic conductivity than the doped lanthanum manganite, but is more expensive and leads to problems, in particular on account of a possible chemical interaction with the electrolyte. 

To ensure good contact resistance (primarily with the cathode) and minimize evaporation of chromia, many developers use interconnect coatings of strontium-doped lanthanum cobaltite or manganite, which have proven effective for at least several thousand hours. 

Yashima, M. and Tsuji, T. (2007) Structural investigation of the cubic perovskite-type doped lanthanum cobaltite Lao.5Sro.4Co03 5 at 1531K possible diffusion path of oxygen ions in an electrode material. /. Appl. 

Deng,J. Zhang,L. Dai, H. et al. Strontium-doped lanthanum cobaltite and manganite highly active catalysts for toluene complete oxidation. Ind. Eng. Chem. Res. 2008, 47, 8175-8183. 

Some perovskite-type oxides having transition elements at B sites exhibit mixed conduction at elevated temperatures. A typical example is doped lanthanum cobaltite, in which oxide ions and holes are charge carriers. The electronic conductivity is a few orders of magnitudes higher than that of the oxide-ionic although the ionic conductivity itself is sufficiently high (>10 S cm at several 100°Q. This kind of mixed conductor is a promising candidate for the electrode materials of SOFCs and ceramic membrane reactors and is described in Chapters 7 and 8 in detail. 

Cathodes present the main electrode issues in designing and operating SOFCs, as described in Chapter 5. Since these operate in a highly oxidising environment, it is not possible to use base metals and the use of noble metals is cost prohibitive. Consequently, semiconducting oxides have been the most prominent candidates since 1966 when doped lanthanum cobaltites began to be used, followed in... 

Magnone, E., Traversa, E. and Miyayama, M. (2005), Synthesis and characterization of strontium and iron-doped lanthanum cobaltite nanocrystaline powders for single chamber solid oxiite fuel cells. Ninth International Symposium on Solid Oxide Fuel Cells (SOFC-IX), Eds. S.C. Singhal and J. Mizusaki, pp. 1617-1626. The Electrochemical Soc. Inc., Pennington, NJ, USA. 

Oxygen diffusion. The total conductivity of Sr-doped lanthanum manganites, cobaltites and ferrites is much higher than the oxygen ionic conductivity. Therefore, to ensure good electrode performances it would be desirable to increase the ionic conductivity (ai) or diffusion coefficients which are interrelated via the Nemst-Einstein relation... 

For lanthanum cobaltites, the formation of La2Zr207 can not suppressed except by lowering the temperature. Hence, rare earth doped ceria is often introduced as the interlayer be-... 

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