Electrolytes perovskites

Perovskites have two possible roles in these cells. The first of these, as a perovskite-derived proton conducting electrolytes, is described earlier (Section 5.3). In cells that use an oxide ion conducting electrolyte, perovskites are mainly employed as... 

Recently a lot of reviews on ionic conductivity of inorganic fluorides were published. A short history of these investigations starting with Faraday s basic work of 1834 up to their current applications is presented in [2]. The structure and ionic conductivity of Pbi xAlxF2+x. Mi x(U or Th)xF2+2x (M = Ca, Sr, Ba, Pb) fluorites and CeFa, Cei yCdyF3 y tysoiutes are described in [5]. In a detailed review [6], various fluoride-conductive electrolytes perovskites MPbF3 (M = K, Rb, Cs), B-deficit perovskites - tysonites... 

Another application is in tire oxidation of vapour mixtures in a chemical vapour transport reaction, the attempt being to coat materials with a tlrin layer of solid electrolyte. For example, a gas phase mixture consisting of the iodides of zirconium and yttrium is oxidized to form a thin layer of ytnia-stabilized zirconia on the surface of an electrode such as one of the lanthanum-snontium doped transition metal perovskites Lai j.Srj.M03 7, which can transmit oxygen as ions and electrons from an isolated volume of oxygen gas. 

A signihcant problem in tire combination of solid electrolytes with oxide electrodes arises from the difference in thermal expansion coefficients of the materials, leading to rupture of tire electrode/electrolyte interface when the fuel cell is, inevitably, subject to temperature cycles. Insufficient experimental data are available for most of tire elecuolytes and the perovskites as a function of temperature and oxygen partial pressure, which determines the stoichiometty of the perovskites, to make a quantitative assessment at the present time, and mostly decisions must be made from direct experiment. However, Steele (loc. cit.) observes that tire electrode Lao.eSro.rCoo.aFeo.sOs-j functions well in combination widr a ceria-gadolinia electrolyte since botlr have closely similar thermal expansion coefficients. 

Electrochemical Promotion of Particulate Matter (Soot) Combustion Using a Ceria-Gadolinia Solid Electrolyte and a Dispersed Perovskite Catalyst... 

The perovskite structure, ABO3 (where A represents a large cation and B a medium-size cation) is adopted by many solids and solid solutions between them can readily be prepared. Vacancy-containing systems with the perovskite structure are of interest as electrolytes in solid-state batteries and fuel cells. Typical representatives of this type of material can be made by introducing a higher valence cation into the A sites or a lower valance cation into the B sites. 

In this chapter the technological development in cathode materials, particularly the advances being made in the material s composition, fabrication, microstructure optimization, electrocatalytic activity, and stability of perovskite-based cathodes will be reviewed. The emphasis will be on the defect structure, conductivity, thermal expansion coefficient, and electrocatalytic activity of the extensively studied man-ganite-, cobaltite-, and ferrite-based perovskites. Alterative mixed ionic and electronic conducting perovskite-related oxides are discussed in relation to their potential application as cathodes for ITSOFCs. The interfacial reaction and compatibility of the perovskite-based cathode materials with electrolyte and metallic interconnect is also examined. Finally the degradation and performance stability of cathodes under SOFC operating conditions are described. 

An alternative to the Co-rich perovskites is the Sr-doped LaFe03 which has a lower thermal expansion coefficient and a superior chemical compatibility with doped Ce02 electrolyte. LaFe03 is expected to be more stable than Ni- and Co-based perovskites because the Fe3+ ion has the stable electronic configuration 3d5. It is, therefore, expected that compositions in the system (La,Sr)(Co,Fe)03 will have desirable properties for intermediate temperature SOFC cathode applications. 

The perovskite oxides used for SOFC cathodes can react with other fuel cell components especially with yttria-zirconia electrolyte and chromium-containing interconnect materials at high temperatures. However, the relative reactivity of the cathodes at a particular temperature and the formation of different phases in the fuel cell atmosphere... 

LaM03 and La, xSrxMO, (M = Co, Ni and Fe) perovskites are relatively unstable compared to their manganese counterparts LaMn03 and La, xSrxMn03. The former compounds readily react with zirconia electrolytes, leading to the formation of secondary phases at temperature as low as 1000°C in air. The Co3+ ions in LaCo03 are... 

To prevent inter-reactions between YSZ electrolytes and perovskite cathode materials [32, 33],... 

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