Effect of titania concentration on the grain boundary conductivity of calcium-doped ceria electrolyte (original) (raw)
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Ionics, 2014
Co-doped samples of Ce 0.95−x Ca 0.05 Sr x O 1.95−x , where (x=0.00, 0.01, 0.02, and 0.03), have been prepared by auto-combustion method and characterized to explore their use as a solid electrolyte for intermediate temperature solid oxide fuel cells (IT-SOFCs). Crystal structure, microstructure, and ionic conductivity have been characterized by X-ray diffraction, scanning electron microscopy, and impedance spectroscopy, respectively. All the compositions have been found to be single phase. Results show that the samples co-doped with Ca and Sr exhibit higher ionic conductivity than the samples singly doped with Ca in the intermediate temperature range. Ce 0.93 Ca 0.05 Sr 0.02 O 2−δ exhibits maximum conductivity among all the compositions. This may be a potential candidate as a solid electrolyte for IT-SOFCs. Keywords Doped ceria electrolyte. Co-doping effect. Ionic conductivity. Solid oxide fuel cells distributed heat-power co-generation, an operation temperature in the range 500-700°C is highly desirable. This is in view of the cost effectiveness because inexpensive stainless steel may be used for this purpose. Doped ceria electrolytes have attracted great interest in recent years because of their potential as a solid electrolyte for intermediate temperature solid oxide fuel cells (IT-SOFCs) application [7]. In CeO 2 , temperature facilitates movement of oxygen ions through oxygen vacancies which are produced in the oxygen sublattice to neutralize the deficiency of charge created by lower valent dopant cations. Doped ceria oxides show much higher ionic conductivity at relatively low temperatures (500-700°C) as compared with yttria-stabilized zirconia. These have been extensively studied as the most promising electrolyte materials for IT-SOFCs. Among the various ceria compositions investigated so far [8-19], Gdand Sm-doped ceria (GDC and SDC) are considered as the most suitable low-temperature solid electrolytes for IT-SOFCs application. Both Gd 2 O 3 and Sm 2 O 3 , however, are very costly. Therefore, there is an increasing interest to develop new cost-effective ceria-based electrolytes. Ceria doped with alkaline earth oxides such as CaO [20, 21] and SrO [22, 23] has been studied extensively. Electrical conductivity of CaO-and SrO-doped ceria is much higher than that of undoped ceria. The highest conductivity was found in the composition Ce 0.90 Ca 0.10 O 1.90 by Shing et al. [24] which is ∼10 −3 S cm −1 at 600°C. Yamashita et al. [25] found that the composition Ce 0.90 Ca 0.10 O 1.90 has the highest conductivity which is ∼10 −2 S cm −1 at 600°C. Banerjee et al. [26] studied the electrical properties of Ce 1−x Ca x O 2−δ (0.05≤x≤0.20) samples prepared by a mixed fuel process followed by sintering at 1,250°C. They found that the composition Ce 0.80 Ca 0.20 O 1.80 exhibits the highest conductivity (1.29×10 −2 S cm −1) at 600°C. Compositions Ce 1−x Ca x O 2−δ with 0.05≤x≤0.20 have been prepared by auto-combustion method and characterized.
Journal of Alloys and Compounds, 2013
Attempts have been made to synthesize a few compositions in the system Ce 0.90 Mg 0.10Àx Sr x O 1.90 (x = 0.00, 0.02, 0.04 and 0.06) by citrate-nitrate auto-combustion method. XRD patterns reveal that all the samples have fluorite crystal structure similar to ceria. Microstructures of samples have been studied by scanning electron microscope. Ionic conductivity of singly doped and co-doped ceria has been investigated as a function of temperature by AC impedance spectroscopy in the temperature range 200-700°C. Impedance plots show a significant decrease in grain boundary resistance after partial substitution of Sr in Mg-doped ceria in the intermediate temperature range. Composition with x = 0.04 shows the highest ionic conductivity (2.0 Â 10 À2 S/cm at 700°C) among all the samples studied. Ó 2013 Elsevier B.V. All rights reserved. 2 (x = 0.30) system which was synthesized by glycine-nitrate process and they found single phase formation in this system and the grain growth of sintered samples was observed to hindered with an increase in Gd content. Composition Ce 0.90 Gd 0.10 O 1.95 was synthesized using combustion technique by Jadhav et al. [14] and they found that the relative density of the sample was more than 90% at 1200°C which was also confirmed by SEM analysis. The grain and grain boundary conductivity of a GDC (Ce 0.90 Gd 0.10 O 1.95
Materials advances, 2022
Towards the development of green energy devices, it is necessary to focus on commercial electrolyte materials for intermediate temperature solid oxide fuel cells (IT-SOFCs). Ca-doped ceria (CDC) samples having a composition of Ce (1Àx) Ca x O 2Àd (0.03 r x r 0.1) were synthesized by a facile solid-state route and sintered at a lower temperature (1473 K). X-ray diffraction, Raman, X-ray photoelectron, Fouriertransform infrared, UV-VIS diffuse reflectance, field emission scanning electron microscopy-energy dispersive X-ray with elemental mapping, and electrochemical impedance spectroscopy techniques were used for the characterization of these CDC samples. The 0.10 CDC showed high oxide ion conductivity of 8.01 Â 10 À3 S cm À1 at 973 K with a lower activation energy of 0.78 eV. The 0.03 CDC, 0.05 CDC, and 0.07 CDC samples exhibited ionic conductivities of 1.66 Â 10 À4 , 4.42 Â 10 À3 , and 5.76 Â 10 À3 S cm À1 at 973 K with activation energies of 1.65, 1.01, and 0.92 eV, respectively. The present work aims to develop Ca-doped ceria as economically viable electrolytes for IT-SOFCs.
Ceramics International, 2020
The gadolinium-doped ceria is investigated as electrolyte materials for intermediate temperature solid oxide fuel cells (IT-SOFCs) due to its oxide ion conductivity. The doping of Gd 3+ to Ce 4+ can introduce a small strain in the lattice thereby improved conductivity with low activation energy is expected. The 20 mol. % gadolinium doped ceria (Ce 0.8 Gd 0.2 O 2− δ) nanocrystalline powder is prepared here by citrate-complexation method. The XRD, Rietveld refinement, FTIR, UV-Visible, FESEM/EDX, and a c-impedance techniques are used to characterize this sample. The oxide ion conductivity is determined between 523 − 1023 K. The Ce 0.8 Gd 0.2 O 2− δ shows highest oxide ion conductivity of 6.79 × 10 − 3 S cm − 1 and 1.11 × 10 − 2 S cm − 1 at 973 K and 1023 K, respectively. The Ce 0.8 Gd 0.2 O 2− δ showed lower activation energies of 1.09, 0.70, and 0.88 eV for grain, grain boundary, and total conduction, respectively. Thus, the nano crystalline Ce 0.8 Gd 0.2 O 2− δ is proposed as potential electrolyte for IT-SOFCs.
ACS applied materials & interfaces, 2017
Samarium doped ceria-carbonate(SDC) has become an attractive electrolyte for low temperature fuel cells because of its impressive ionic conductivity and high performance. Different doped ceria-carbonate (SDC-single, SDC-binary, and SDC-ternary) electrolytes were synthesized by the co-precipitation/oxalate method, to optimize the electrochemical performance. The structure, morphology, and thermal, optical, and surface properties, have been studied using a variety of techniques. These include x-ray diffraction, scanning electron microscopy, thermogravimetric analysis, UV-visible absorption spectroscopy, and Fourier infrared spectroscopy. The x-ray diffraction results confirmed the successful incorporation of samarium into ceria as a crystalline and inclusion of carbonate is an amorphous nature. To analyze the conduction mechanism, dc conductivity was measured in a H2/O2 atmosphere. Doped ceria-binary carbonate (Li/Na)CO3-SDC) showed the highest ionic conductivity of 0.31 S cm-1, and p...
Structural and Ionic Conductivity Studies of Doped Ceria Electrolyte
Electrochemical and Solid-State Letters, 2012
The present study reports synthesis, XRD, Impedance spectroscopy and ionic conductivity of Ce 1−x (Gd 0.5 Pr 0.5) x O 2 (x = 0-0.24) system. These samples were synthesized through the sol-gel process followed by low temperature combustion. The samples were sintered at 1300 • C to obtain dense ceramics (over 98%). XRD confirms the single phase with a cubic structure. The two-probe a.c. impedance spectroscopy was used to study the ionic conductivity of doped ceria samples. The Ce 0.88 (Gd 0.5 Pr 0.5) 0.12 O 2 , Ce 0.84 (Gd 0.5 Pr 0.5) 0.16 O 2 compositions showed highest grain ionic conductivity values i.e., 1.012 × 10 −2 S/cm and 1.059 × 10 −2 S/cm respectively at 500 • C.
Research Journal of Chemistry and Environment, 2021
The search for new cost-effective electrolyte materials for IT-SOFC towards its mass scale commercialization has gained momentum in recent years. The Ca-doped ceria having composition Ce0.91Ca0.09O2 was prepared using the facile conventional solid-state method. The structural and electrical properties of low sintered ceramic samples have been characterized by X-ray diffraction (XRD), UV-VIS diffuse reflectance spectroscopy (DRS) and A.C. impedance technique respectively. The oxide ion conductivity was measured between the temperatures 573 K−973 K in air. The obtained results showed that total conductivity is mainly dependent on the grain boundary effect. The nanocrystalline Ce0.91Ca0.09O2 exhibited the high total ionic conductivity of 7.36 10 3 S cm 1 at 973 K with a lower activation energy of 0.96 eV. The obtained results highlight the use of cost-effective dopant in ceria lattice to develop commercially viable electrolyte materials for IT-SOFC.
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...
The Ce0.9Gd0.1O2‐δ ceramics with 500 ppm SiO2 and with the different dopant of Zn (0.5, 1.0, 2.0, 3.0 at.%) were prepared by sol‐gel method. All the materials were single phase with a cubic fluorite structure. The relative densification reached a maximum at 1.0 at.% ZnO sintering at 1500 ℃ for 12 h. The conductivities showed sharp increase for the ceria system that contained of ZnO in the range of 0.5 to 1.0 at.% and beyond 1.0 at.%, the conductivity slightly decreased. For the solution adding 1.0 at.% ZnO had the highest total conductivity and grain boundary conductivity ( t = 3.8×10 ‐3 S • cm ‐1 , gb = 3.3×10 ‐2 S • cm ‐1 at 550 ℃) compared to the ceria system without ZnO ( gi = 2.4×10 ‐3 S • cm ‐1 , gb = 6.4×10 ‐3 S • cm ‐1 at 550 ℃).
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 (