Lanthanum strontium ferrites

In FC and electrolysis operating modes, the performance of the oxygen electrode decreases in the order lanthanum strontium cobalt ferrites (LSCFs) > lanthanum strontium ferrites (LSFs) > lanthanum strontium manganites (LSMs). The degradation stability of LSCFs and LSFs in electrolysis mode is better than that of LSMs and YSZ. 

Strontium cobalt ferrites are good mixed conductors but are more suitable to be used as cathodes due to their p-type conduction. Pervoskite gaUates/niobates/barium cerate and chromium-doped lanthanum-strontium ferrite have also been studied as the anode material. Although the gaUates and niobates exhibit low conductivity, they exhibit good compatibihty with the LSGM electrolytes. The conductivity of yttrium-doped barium cerates increases by increasing yttrium content. For barium cerates, the increase in electronic conduction due to the reduction of cerium at low... 

Chang, H.C., Tsai, D.S., Chung, W.H., Huang, Y.S., Le, M.V. A ceria layer as diffusion barrier between LAMOX and lanthanum strontium cobalt ferrite along with the impedance analysis. Solid State Ionics 2009,180, 412-7. 

In many cases, achievement of reliability is in trade-off relation to cost reduction. To overcome this, it is required to make breakthroughs in the fabrication technologies. Cells to be operated in the temperature region of around 800°C. Metal intercoruiects are used together with anode-support cells and sealing materials. The active cathode such as LSCF (lanthanum strontium cobaltite ferrites) is used so that the durability is one of the main issues. 

Table 18.2 Comparison of cathodes among lanthanum strontium manganites, ferrites, and cobaltites in their chemical reactivity, functionality as cathode, and tolerance against Cr poisoning...

The current state-of-the-art SOFC anode-supported cells based on doped zircona ceramic electrolytes, ceramic LSM cathodes, and Ni/YSZ cermet anodes are operated in the temperature range 700-800°C with a cell area specific resistance (ASR) of about 0.5 O/cm at 750°C. Using the more active ceramic lanthanum strontium cobalt ferrite (LSFC)-based cathodes, the ASR is decreased to about 0.25 Q/cm at this temperature, which is a more favorable value regarding overall stack power density and cost-effectiveness. 

Anode - Reaction site for oxidation of water (creation of O2) - Porous layer (to facilitate the evacuation of the gas produced) - Perovskite-type oxide - The materials typically used are LSM (LaSrxMni.x03) or LSCF - Many other alternatives are possible - LSM = Lanthanum strontium manganite -LSCF = Lanthanum cobalt strontium ferrite... 

Strontium-doped lanthanum manganite, La1 3.Sr3.MnO3 (LSM) is developed by doping lanthanum manganite with a small fraction (10%-20%) of strontium in order to enhance electronic conductivity of the cathode electrode. Lanthanum strontium cobalt ferrite (LSCF) is a mixture of lanthanum oxide, strontium oxide, cobalt oxide, and iron oxide with typical composition given as Lao eSro iCoo Fco sOs. 

The experiments were performed on an anode supported planar Solid Oxide Fuel Cell which consists of a 525—610 pm thick anode with two layers (both made of MO/8YSZ cermet functional layer 5—10 pm thick support layer 520—600 p thick) a 4—6 pm thick dense electrolyte Yo,i6Zro.g402 (8YSZ) a 2—4 pm thick barrier layer made of yttria doped ceria (YDC) the cathode consists of a 20—30 pm thick layer made of porous lanthanum strontium cobalt ferrite oxide... 

LSCF lanthanum strontium cobalt ferrite, (La,SrXCo,Fe)03... 

Adequate electronic and ionic conductivity. Though the conductivities are adequate, the ionic conductivity of LSM is significantly lower than YSZ, and its electronic conductivity is a fraction of any of the metals or even of lanthanum chromite. Consequently, ionic and electronic resistance can become a significant factor, especially in cell designs that incorporate long current paths through the cathode. For lower-temperature cells, conductivity of LSM is inadequate, and other materials, such as strontium-doped lanthanum ferrite (LSF) are considered. 

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