(a) O2 −-ion energies (filled circles) and oxygen-vacancy energies for ordered and disordered partial occupation of a set of sites that are crystallographically equivalent if the ions are disordered. Despite the discovery of a large number of oxide ion conductors in crystals or ceramics such as ZrO2-Y2O3 (YSZ), LaGaO3(LGO), etc., as discussed in Section 7.2, no oxide ion conductors have been reported in glassy materials except in some recent research by Angell's group.234. For instance, ceria and the increasingly important ceria-zirconia system serve as fast oxygen storage compounds for exhaust gas catalysts. it must be chemically and mechanically compatible with the other components of the cell (cathode and anode), with close thermal expansion coefficients to avoid delamination when heating the cell. However, at low temperatures, the oxide ion conductivity of La1.61GeO5–δ becomes much smaller because of the change in activation energy. Photoelectron emission microscopy (PEEM) yields information on the local work function (Casalis et al., 1995) and scanning photoelectron microscopy (SPEM) gives the local surface composition (Von Oertzen et al., 1991). By continuing you agree to the use of cookies. it must be stable under oxidizing and reducing atmospheres. These requirements imply that defects are present in the crystalline structure to allow oxide ion diffusion, a careful choice of elements to avoid any risk of reduction under hydrogen and optimization of the phase preparation, properties and sintering conditions. Oxide-ion conductivity of doped ZrO2 at 1000 °C as a function of dopant level (X). Is it ok to eat a frozen turkey with black spots on it? Therefore, high thermodynamic efficiency is achieved and coking is not a problem. An oxide ion has a negative two charge (-2) The sodium ion has a 1+ charge and the chloride ion has a 1- charge. The electronic properties of ZrO2- based electrolytes are vitally important to the loss of fuel and therefore the electrical efficiency of an SOFC. The temperature dependence of oxide-ion conductivity σVO•• of isotropic ZrO2-based materials has been described by random-walk theory84 in Chapter 5; it is further elaborated into the Arrhenius form by combining equations [5.5] and [5.7], For a fluorite unit cell, l = a/2 (a is the lattice parameter), w = 6, f ≈ 1, N = 4a− 3, q = 2e, equation [12.2] reduces to, Equation [12.1] suggests that the activation energy can be obtained from the slope of a plot of ln σVO¨T versus 1/T. 5.2. This information is useful in developing the oxide ion conductor glass described below. Depending upon temperature and partial pressure of oxygen, PO2 the conduction could result from contributions of oxide-ions and electrons, the latter either in the form of electron holes or excess electrons. The details on how to evaluate the effect of electronic conductivity on electromotive force (EMF), leakage current density, and electrical efficiency can be found in Chapters 4 and 8. Another possibility is that Ca that has already been deposited can react with O2 to provide the necessary fraction of CaO in the CaZrO3 composition. Such a change in activation energy with temperature is often revealed by a kink at a characteristic temperature or a gradual curvature over a temperature range in the Arrhenius plot of oxide-ion conductivity. All of these features make it possible to construct a fuel cell of unprecedented electrical efficiency when operated on hydrocarbon fuels. The reaction can occur before or after deposition, but again one would expect the species in the plume to be more reactive than those deposited already. An oxide ion is a negatively charged oxygen atom. 10.18. Photoelectron spectroscopic techniques have been greatly improved with respect to lateral resolution. The main role of an electrolyte in a SOFC is to allow the conduction of the oxide ions O2− from the cathode to the anode without allowing the transport of electrons, to avoid any risk of current leakage. Also included for comparison are the defect reactions for CeO 2 - … Comparison of the oxide ion conductivity in La10Si6O27 and Nd10Si6O27−based oxide with conventional oxide ion conductors. At 700 °C the OCV and the peak power density of a cell with 20 μm thick BCNO electrolyte were 0.950 V and 315 mW cm−2, respectively. What is the charge on each cobalt ion?The total oxide ion charge in a formula unit of Co2O3 is 6-. We have used the LIV-MS facility to characterize the plume formed under PLD conditions to understand the optimal conditions required to get good-quality thin films. Therefore, it is generally believed that the high symmetry in the lattice is an essential requirement for fast ion conduction. However, the large coordination number around the cations allows the fluoride anion to move in glasses. Oxide-ion conduction requires either the introduction of interstitial oxide ions, Oi2 −, in an array of empty interstitial sites at some higher energy, and/or mobile oxygen vacancies in the array of occupied sites.