Perovskite-type materials SOFCs electrolytes

Various perovskite-type oxides [133, 134], as well as Ba2lii205 [135-137], and LaioGeg027 [120, 138,139] exhibit protonic conductivity. Among these materials, the perovskite-type oxides show outstanding protonic conductivity. To mention a few, SOFCs with BaCeo.gYo.203 5 solid electrolytes can be operated at low temperatures above 400°C [140, 141], and a power density of 100 mW/cm at 500°C has been achieved (Fig. 6.11, [141]). 

The flexibility of the perovskite crystal structure and the opportunity to accommodate various dopants offer the possibihty to tailor material properties. The design of catalytic or electronic properties, such as ionic or electronic conductivity, is in the focus of solid oxide fuel cell (SOFC) research activities. Perovskite-type oxides are therefore a well-investigated class of materials and commonly applied as functional layers in SOFCs, as porous microstructured cathode layer on the air electrode side [32-36] and very recently as anode on the fuel side [35]. On a research level, perovskite-type oxides are also apphed as gas-tight electrolyte to separate anode and cathode compartments [37,38] or as an interconnector material [39,40]. Beside the stoichiometry and crystal structure, processing... 

Perovskite-type Sr-doped LaMnOs (Lanthanum Strontimn Manganites- LSM) has particularly attracted substantial interest as a promising material for cathode in SOFCs. This material has good properties such as chemical and thermal stability, and high catalytic activity for oxygen reduction. Additionally, it has a thermal expansion coefficient similar to that of a solid electrolyte (YSZ), and high electronic conductivity [2]. 

Hence, by the combination of structural and transport properties, LSiF-LSNF nanoeomposite appears to be promising as cathode material for SOFC with apatite-type eleetrolyte provided the sintering temperature is below 1200 °C. The most promising approach consists in application of this composite as thin functional interlayer between the eleetrolyte and thin porous perovskite layer comprised of the same LSNF or other complex perovskite. This will help to mateh the thermal expansion coefficient of cathode and eleetrolyte as well as prevent too strong interaction between perovskite and electrolyte if sintering temperature will be high. 

Cathode materials for SOFCs based on any of the electrolytes described in Section 2.1.1 are of the perovskite structure type, generally La-based with transition metals located on the B site. Several authors " have summarised the range of perovskites investigated to date, concentrating on the conductivity, ion transport and compatibility of these materials. As such it is superfluous to continue the discussion in detail here. Instead we will refer to the main cathode types only, leaving the reader to consult the relevant literature for further details. 

An alternative approach to reduce the operating temperature is to use new electrolyte materials such as scandium doped zirconia (SeSZ), and rare earth doped ceria (RDC) which have the fluorite type stmeture, or lanthanum gallate based oxides such as (La,Sr)(Ga,Mg)03 (LSGM) with perovskite stmeture, all of which have higher ionic conductivities than YSZ. An 1 kW class SOFC stack with (La,Sr)(Ga,Mg,Co)03 electrolyte was demonstrated by the collaboration of Mitsubishi Materials Corp. and The Kansai Electric Power Co., Inc. in 2001,... 

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