Silica-scavenging effects in ceria-based solid electrolytes (original) (raw)
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Ceria-based solid electrolytes
Solid State Ionics, 1996
Ceria-based solid electrolytes are reviewed in terms of electrical conductivity, diffusivity and transference number. The electrical conductivity and diffusion constants of various fluorite compounds are compared and those of ceria-based oxides are almost the highest among these fluorite oxides. The electrical conductivity of doped ceria is much dependent on the kind and the concentration of dopants. The reason for this behavior and a guideline to obtain more electrically conductive materials are discussed. The effect of sample preparation on the electrical conductivity is described in terms of the character of raw materials, impurities and the sintering condition. The factors to determine the transference number and the methods to increase the transference number at low oxygen pressures are also discussed.
Role of salts on the electrical performance of ceria-based electrolytes: An overview
Frontiers in Materials
This work provides an overview on established achievements and debatable findings involving Ca, Gd or Sm-doped ceria-based electrolytes, using Li2CO3, LiNO3 and Na2CO3 as sintering aid or as second phase. The performance of these materials is discussed considering the characteristics of the oxides and of the salts or derived second(ary) phases (e.g., alkali metal oxides and hydroxides, eutectic mixtures), extensively surveyed to identify influential parameters with respect to processing and electrical performance (e.g., melting and boiling points, thermal decomposition, hydrolysis). The analysis of published data highlights the possible contribution of additional charge carriers to the total conductivity, besides oxide-ion vacancies. Claimed bulk and grain boundary conductivity enhancements are deeply discussed, as well as advantages and limitations of impedance spectroscopy as characterization tool. Irrespective of controversial reasons, reports on unusual improvements of grain bou...
Effect of co-dopant addition on properties of gadolinia-doped ceria electrolyte
Journal of power sources, 2000
. Various trivalent oxides were added as co-dopants to gadolinia-doped ceria GDC electrolyte used for solid oxide fuel cells at up to 5 mol%. An examination was made on how they affect the electrical conductivity of the electrolyte and, eventually, the open-circuit voltage Ž . Ž . OCV of a unit cell. Through a comparison of the thermal expansion coefficients TEC , it was investigated whether or not the co-doped electrolytes are thermomechanically compatible with other cell components. The addition of co-dopants generally improve the electrical Ž . properties of the electrolyte by yielding greater OCV values and not changing the TEC significantly 5% at most , except in the case of Ž . Pr. Among the electrolytes examined, the one co-doped with Sm 3 mol% shows the best improvement in performance. q 2000 Elsevier Science S.A. All rights reserved.
Journal of Solid State Electrochemistry, 2004
We have prepared pure electrolytes of Ce 0.8 Gd 0.2 O 1.9 (CGO) and Ce 0.8 Sm 0.2 O 1.9 (CSO), useful for SOFCs, by a sol-gel-related technique like the acrylamide method. This method consists of preparing a solution from the single oxides followed by gelation. Then, the combustion or decomposition of the organic molecules is initiated, producing nanometric calcined powders of the above-mentioned compounds. Thermal treatments were optimized in order to obtain good electrochemical properties of the electrolytes. We have observed that the synthesis temperature to obtain the pure phase is lower for the sol-gel samples than for the pellets prepared by solid-state reaction, and the final density is higher. The microstructure and composition of the powders were characterized by TEM, SEM, and EDX analysis. The electrical properties of the electrolytes were measured by impedance spectroscopy at different temperatures and oxygen partial pressures.
Journal of Applied Biomaterials & Functional Materials, 2016
Doping the crystalline structure of CeO 2 with R 3+ ions of rare earth metals (Gd 3+ , Sm 3+ , Nd 3+ , Y 3+ , Pr 3+) causes a remarkable increase in ionic conductivity. This increment is ascribed to a modification in the crystalline lattice, represented by the increase of O 2vacancies, so that a large number of anion defects arises (6-8). Gadolinium ion, Gd 3+ , is the most extensively studied dopant for ceria in solid electrolytes application for SOFCs (9-12). The traditional synthesis techniques for these materials has achieved excellent results, but an extended time for complete reaction is required (13-17). Furthermore, the performance of solid electrolytes can be affected by many factors such as doped composition material, thickness, microstructure and the temperature at which the electrolytes are to be used (18). The microstructure of a sintered material depends mainly on the synthesis methods and conditions used (19). From this point of view, liquid phase syntheses, such as hydrothermal synthesis (20-23), sol-gel (24-27) and combustion synthesis (28-30) are very interesting for realizing nanosized powders. Synthesis procedures play a critical role in the final particle size (31) and consequently have an influence on the
Study on La and Y co-doped ceria-based electrolyte materials
Journal of alloys and …, 2007
Co-doped ceria electrolytes of Ce 0.8 La 0.2−x Y x O 1.9 (x = 0.02, 0.06, 0.10, 0.14, 0.20) fine powders were prepared with the sol-gel method. The results of X-ray diffraction and Raman spectroscopy showed that all powders crystallite calcined at 800 • C were single phase with cubic fluorite structure, the average crystallite sizes calculated by the Scherrer formula were between 27 and 34 nm, which was in good agreement with the results of TEM and particle size distribution measurements. The thermal expansion curves of Ce 0.8 La 0.2−x Y x O 1.9 were measured and the thermal expansion coefficients (TEC) between 100 and 800 • C were calculated. For the samples of Ce 0.8 La 0.2−x Y x O 1.9 , in the temperature range of 700-850 • C, when x = 0.06, 0.10 and 0.14, much higher ionic conductivity was observed than those of the singly doped ceria with same dopant concentration (20% trivalent rare earth) and when x = 0.06, maximal conductivity is obtained. It suggested that co-doping with appropriate ratio of lanthanum and yttrium can further improve the electrical performance of ceria-based electrolytes, and these co-doped samples may be the better electrolytes for intermediate-temperature solid oxide fuel cells. of oxygen vacancy, and therefore lower the activation energy of conduction and improve the ionic conductivity. And Kim found that the reduction of the lattice deviation of the doped ceria from the pure ceria would lead to the reduction of the lattice strain of the doped ceria, therefore, lead to the decrease of the activation energy of conduction and the increase of the ionic conductivity of the doped ceria. Up to now, some co-doped ceria-based electrolytes have been investigated, such as (
Influence of the nature of the contact electrode on the conductivity measurements of doped ceria
Gadolinia doped ceria powders were prepared by the oxalate coprecipitation technique and pellets of these powders were sintered for 10 h at 1400°C. The impedance spectra were taken at temperatures ranging from 150°C to 800°C with different contact electrodes. Gold, platinum and silver from commercial paints and inks as well as sputtered platinum and La 0.8Sr 0.2Co 0.8Fe 0.2O 3 were used as contact electrodes. The total conductivities at temperatures higher than 500°C were roughly the same except when sputtered platinum electrodes were used. At lower temperatures, however, there is significant difference in the conductivity. While the grain interior resistivities are approximately the same regardless of the electrode nature, the grain boundary resistances are strongly influenced by the electrode nature
Journal of The European Ceramic Society, 2011
Composite electrolytes with nominal compositions, Ce 0.8 Gd 0.2 O 1.9 + xBaO (x = 0.2 and 0.3), have been synthesized through the citrate route. Formation of two phases, namely Gd-doped ceria and Gd-doped barium cerate, has been confirmed through XRD and SEM studies. The impedance spectra show three distinct semi-circles, all originating from the composite electrolytes. In the temperature range 175-350 • C, the activation energies for the conductivity values extracted from the high frequency and intermediate frequency parts of the impedance spectra remains the same, irrespective of compositional and micro-structural variation. On the other hand, the activation energies for the conductivity values associated with the low frequency impedance spectra show a significant change with micro-structural variation. Solid oxide fuel cells constructed using these composite electrolytes exhibit a higher open circuit voltage compared to those based on single phase 20 mol% Gd-doped ceria.
CERAMICS INTERNATIONAL Electrical properties of multidoped ceria
Multidoped nanosized ceria powders were prepared by either modified glycine nitrate procedure (MGNP) or self-propagating reaction at room temperature (SPRT). As the dopants to CeO 2 , trivalent rare earth oxides such as Nd 2 O 3 , Sm 2 O 3 , Gd 2 O 3 , Dy 2 O 3 and Y 2 O 3 were used, with the total molar fraction of 20%. The pressed powder pellets were subjected to the densification by sintering at 1500 1C, in an air atmosphere. A single-phase crystalline form was evidenced by X-ray diffractometry for both sintered materials. By means of complex impedance measurements, the conductivity of the sintered samples was determined as a function of temperature. At 700 1C, the conductivity amounted to 2.19 Â 10 À 2 and 1.40 Â 10 À 2 Ω À 1 cm À 1 for the SPRT and for the MGNP sample, respectively. The corresponding values of activation energies of conductivity amounted to 0.72 (MGNP) and 0.59 (SPRT) eV in the temperature range 550–700 1C.
A modified sol–gel method which is also known as citrate complexation is used here to prepare Ce 0.8 Ln 0.2 O 2Àd (Ln = Y 3+ , Gd 3+ , Sm 3+ , Nd 3+ and La 3+) solid solutions for their proposed application in intermediate-temperature solid oxide fuel cells (IT-SOFCs) as electrolytes. All the samples exhibit the fluorite type crystalline structure without any phase segregation, characteristics of CeO 2 , as revealed in XRD pattern. The lattice parameters and densities calculated based on the oxygen vacancy model agreed well with the experimental (Archimedes method) values. The formation of solid solution is also confirmed by Raman spectroscopy. The microstructural features of the samples are recorded by using FE-SEM/TEM. The ionic conductivities of various Ln-doped samples at 623 K as obtained from electrochemical impedance measurement are as follows: Ce 0.8 Sm 0.2 O 2Àd > Ce 0.8 Gd 0.2 O 2Àd > Ce 0.8 Nd 0.2 O 2Àd > Ce 0.8 La 0.2 O 2Àd > Ce 0.8 Y 0.2 O 2Àd. The activation energy for total conductivity are found to be 0.86, 0.87, 0.89, 0.96 and 1.02 eV for Sm, Gd, Nd, La and Y doped ceria, respectively. The relationship between the dopant radius, chemical composition , lattice parameters, morphology and electric properties are discussed here.