Lanthanum-based materials

Magnesia and lanthanum based materials are the most effective of the samples tested to date. 

The interconnect material is in contact with both electrodes at elevated temperatures, so chemical compatibility with other fuel cell components is important. Although, direct reaction of lanthanum chromite based materials with other components is typically not a major problem [2], reaction between calcium-doped lanthanum chromite and YSZ has been observed [20-24], but can be minimized by application of an interlayer to prevent calcium migration [25], Strontium doping, rather than calcium doping, tends to improve the resistance to reaction [26], but reaction can occur with strontium doping, especially if SrCr04 forms on the interconnect [27],... 

Fergus JW. Lanthanum chromite based materials for solid oxide fuel cell interconnects. Solid State Ionics 2004 171 1-15. 

Two of the materials were furnished by catalyst companies and are referred to as magnesia-based or magnesia and lanthanum-based or lanthanum. These latter materials are both known to contain cerium and alumina as well. 

Figure 17 shows a comparison of the fresh SO2 removal ability for these five major types of commercially available SOx catalysts. The materials were tested at 1350 F at various concentrations with a very low capacity cracking catalyst. The magnesia-based catalyst is much better than lanthanum-based catalyst followed by platinum or cerium on alumina and finally alumina alone. The reverse order in activity observed for the lanthanum-based and cerium additives, compared to the relative results given previously for lanthanum and cerium, was not investigated, but may be related to the presence of cerium on the lanthanum-based additive (27). 

Commercial catalysts vary in the degree to which they are regenerable at reactor temperatures as shown on Figure 18. The initial SO2 removal for all five materials was adjusted to an equal basis by varying the amount of additive used 0.8% magnesia-based, 3% lanthanum-based, 10% of both cerium/alumina and... 

The discovery of high-temperature superconductivity in a lanthanum-based cuprate perovskite material with a transition temperature of Tc = 35 K by Bednorz and Muller... 

The fluorine sensor is extensively used conunerdally. The fluorine content can also be detected by chemical sensing and the principle of this device also belongs to type II. The base material is lanthanum fluoride, which is an excellent fluorine conductor, and which is stable even in aqueous solution. A typical plication is to measure the fluorine content in test water solutions. The principle of fluorine detection is based on the F concentration cell method. The detection limit is as low as 10 M, which covers most F" concentrations in drinking water. A fast response is one of the typical characteristics of the type-II sensor it is less than 3 minutes even if the F content is as low as 10" M. 

The base material used as a solid electrolyte is lanthanum fluoride. In the fluoride, the only permeable carrier is the fluorine anion in the single-crystal membrane. The inside of the tube is filled with a standard fluoride solution (Lingane 1967) and, when the sensor is... 

One other rare-earth application is their direct use as a base material of the sensor. One typical application is with rare-earth fluorides. The fluorides are excellent fluorine ionic conductors even at room temperature and also very stable in an aqueous solution. These features make the commercial use in fluorine sensing in a solution possible. A practically used material is lanthanum fluoride. Other rare earths also show similar... 

A base material used for alcohol sensing is the perovskite oxide with rare-earth elements, which shows p-type semiconducting properties. The most commonly used rare earth is lanthanum. In this case, to retain a perovskite structure with semiconducting characteristics is important. Other rare earths are used instead of lanthanum. However, lanthanum is the most reasonable choice of the rare-earths series from the expense viewpoint. Methane sensing is also attempted by using the rare-earth-containing perovskite oxide. The perovskite oxide does not act as base material but as the auxiliary electrode to accelerate methane combustion. 

The ceramic-type interconnect commonly used for planar SOFCs is based on lanthanum chromite. Recently, a LaxCai.xCryCoj.yOj solid solution has been developed. It is readily sintered in air at 1350 to 1500°C and appears to have superior stability and electrical properties compared to previous lanthanum chromite materials. Densities greater than 95% of theo-retieal are routinely achieved. The interconnect is machined into the desired shape to form the channels for gas flow. Figure 12.30 shows a sectional view of a 25-cell stack of 10 x 10 cm and its performance. A maximum output of 421 W is obtained. 

For perovskite-based fuel electrodes, Mn-doped lanthanum strontium chromite (Lao.75Sro25Mno.5Cro.5O3, LSCM), developed by Tao and Irvine, has been infiltrated with ceria-based materials by other research groups, who reported that an improved electrocata-lytic activity was achieved when tested with various fuels. " Without infiltration of a ceria phase into LSCM-YSZ anodes, the oxidation of methane was considered to be limited by insufficient oxygen ion conductivity in the lanthanum chromite-based materials. Gd-doped ceria has higher oxide ion conductivity than LSCM, which is also illustrated by an improved performance of these infiltrated electrodes. The mechanism of methane oxidation in Gd-doped ceria-infiltrated LSCM anodes in wet CH4 was considered to involve the partial oxidation of methane by a gas/solid reaction between ceria and methane-generating CO and H2, followed by electrochemical oxidation of the products. The added ceria also suppressed coke formation in these anodes. ... 

---