Solid electrolyte perovskites

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... 

G. Ch. Kostogloudis, Ch. Ftikos, A. Ahmad-Khanlou, A. Naoumidis, D. Stover, Chemical compatibility of alternative perovskite oxide SOFC cathodes with doped lanthanum gallate solid electrolyte , Solid State Ionics 134,127-138 (2000). 

On the other hand, the theoretical performance of concentration electrochemical cells, based on perovskite materials with protonic and oxygen ion conduction properties, has been described as well [191]. Besides, a sensor for the detection of oxidizable gases that employs the production of a non-Nemstian electrode potential, using zirconia as the solid electrolyte, has been developed [192],... 

In general, although surface protonation of perovskite oxides in contact with aqueous electrolytes and consequent build up of a potential barrier at the oxide surface under cathodic polarization represents a serious drawback, perovskite oxide electrodes are good candidate electrocatalyst materials in molten carbonate [390] and high-temperature solid electrolytes [391],... 

The basic elements of a SOFC are (1) a cathode, typically a rare earth transition metal perovskite oxide, where oxygen from air is reduced to oxide ions, which then migrate through a solid electrolyte (2) into the anode, (3) where they combine electrochemically with to produce water if hydrogen is the fuel or water and carbon dioxide if methane is used. Carbon monoxide may also be used as a fuel. The solid electrolyte is typically a yttrium or calcium stabilized zirconia fast oxide ion conductor. However, in order to achieve acceptable anion mobility, the cell must be operated at about 1000 °C. This requirement is the main drawback to SOFCs. The standard anode is a Nickel-Zirconia cermet. 

Bonanos, N., Knight, K.S., and Ellis, B., Perovskite solid electrolytes Structure, transport properties and fuel cell applications. Solid State Ionics, 79, 61,1995. 

Kuchynka et al. [125] studied the electrochemical oxidative dimerization of methane to C2 hydrocarbon species using perovskite anode electrocatalysts. Three designs of solid oxide fuel cells were used, including tubular and flat plate solid electrolytes. The maximum current density for the dimerization reaction at these electrocatalysts was related to the oxygen binding energies on the catalyst surface. The anodic reaction was ... 

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. 

Other oxygen ion conductors that have potential use as solid electrolytes in electrochemical devices are stabilized bismuth and cerium oxides and oxide compounds with the perovskite and pyrochlore crystal structures. The ionic conductivity and related properties of these compounds in comparison with those of the standard yttria-stabilized zirconia (YSZ) electrolyte are briefly described in this section. Many of the powder preparation and ceramic fabrication techniques described above for zirconia-based electrolytes can be adapted to these alternative conductors and are not discussed further. 

R.L. Cook and A.F. Sammells, On the systematic selection of perovskite solid electrolytes for intermediate temperature fuel celk. Solid State Ionics, 45 (1991) 311-321. 

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... 

Figure 9.5 Comparison of the oxygen ionic (a) and electronic (p- and n-type) (b) conductivity of selected solid electrolytes and mixed conductors under oxidizing conditions. The partial ionic conductivity of perovskite-type...

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