Electrolytes perovskite structure

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. 

Certain oxides with a perovskite structure are generally applied to the cathode. For high temperature type SOFCs, doped-LaMn03 is used as the typical cathode. For low temperature SOFCs, LaSr(CoFe)03 or La(NiFe)03 are used as the cathode. Doped LaCo03 has a high electric conductivity and shows an excellent catalytic performance. However, the TEC of LaSrCo03 is larger than that of the electrolyte, and so Fe is substituted to reduce the TEC of the cathode. 

Perovskite-structured oxides with high electronic and oxygen ion conductivities could be used as a membrane alternative to solid electrolytes for oxygen separation. In such materials, both oxygen ions and electronic defects are transported in an internal circuit in the membrane material. 

In the search for new oxygen ion conductors to be used as electrolytes in SOFCs, oxides have been extensively studied in recent years, which crystallize in the perovskite structure and in structures derived therefrom e.g. the brownmillerite... 

Perovskite (ABO3 in which A is divalent and B is tetravalent) and pyrochlore (AaBaOi in which A is trivalent and B is tetravalent) oxide compounds have been proposed as oxygen ion conducting electrolytes for electrochemical devices. Some of the perovskite structures (e.g., BaCeO and SrCeOs) are generating interest because of... 

Many perovskite-structured oxides exhibit high oxide-ion conductivities at elevated temperatures, and have attracted significant interest for use as sohd electrolytes in, for example, SOFCs (see Chapters 9, 12 and 13). The compounds can be divided into camps with compositions or A + B + O3, of which LaGaO3 and... 

In 2000, the details of a new trivalent Y ion-conducting solid electrolyte with an A-site-defident perovskite structure, Y (Ta3 Wi 3jO3 (0<%<0.33) [115], were reported. By substituting the pentavalent Ta site for hexavalent W in Yi/rTaOj, A-site cations (such as Y +) could be completely moved into alternate layers, and Y +vacancies introduced. In the Y (Ta3xWi 3x)O3 series, Yo.o6(Tao.i8Wo.82)03 (x —0.06) exhibited the highest conductivity (ca. 2.6 x 10 Scm at 362 °C), this... 

Solid oxide electrolyzer cells (SOEC) have a solid oxide ion conductor as electrolyte, often yttria-stabilized zirconia (YSZ). The cathode (CO evolution, negative) is often a Ni-YSZ composite called a cermet. The anode (O2 evolution, positive) most often consists of a composite of YSZ electrolyte and an electron-conducting perovskite-structured oxide, e.g., (Lao.75Sro.25)o.95Mn03 [1]. 

Lithium can be inserted into the material up to at least 0.08 Li" " per formula unit. This level of intercalation is insufficient for the number of lithium and lanthanum cations to exceed unity and so the A sites of the perovskite structure still contain some vacancies at this stoichiometry. Whilst this intercalation process is reversible, experiments using this electrolyte in conjunction with a graphite electrode show that an irreversible oxidation process occurs. The reduction of Ti" " narrows the band gap and leads to electronic conductivity of 0.01 S cm at room temperature. This reactivity and electronic conduction would lead to a rapid discharge via short circuit of a stored battery and so makes these materials unsuitable for use as an lithium electrolyte in these applications. 

A related study has been performed on perovskite-structured oxides for possible use as cheap hydrogen membranes and electrolytes for solid oxide fuel cells (SOFC). SOFCs have demonstrated excellent fuel efficiency and versatility, but the short operational lifetime of any fuel cell remains a major hindrance for commercial utilization [68]. Several factors contribute to... 

However, reliable information about dependence of the functional properties of complex nickelates on their chemical composition and structure is still absent, while any straightforward and accelerated design of cathode materials is to be based upon reliable (and independent upon their interaction with electrolyte) characterization of the ability of then-surface sites to catalyze the oxygen reduction as well as of oxygen mobility in the bulk. Several lanthanum-nickel-iron mixed oxides with perovskite structure have demonstrated promising performance as cathodes for IT SOFC with traditional YSZ and GDC electrolytes [111-112]. However, studies of the behavior of electrode materials in contact with ATLS electrolytes or that of ATLS-based composites are veiy scarce [113]. 

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... 

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