Thermodynamic Stability of Gadolinia-Doped Ceria Thin Film Electrolytes for Micro-Solid Oxide Fuel Cells (original) (raw)
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Investigation of the stability of ceria-gadolinia electrolytes in solid oxide fuel cell environments
Solid State Ionics, 1999
Doped ceria-based materials are potential electrolytes for use in lower operating temperature (500-700 o C) solid oxide fuel cells because of their high ionic conductivity. In this study, impedance behaviour and microstructure of the (Ce 0.8 Gd 0.2)O 1.9 exposed to mild fuel environments (H 2-N 2 mixtures) have been investigated. The exposure of specimens to H 2-N 2 mixtures at 1000 o C resulted in a substantial expansion of the lattice as a consequence of the reduction of Ce 4+ to Ce 3+ , which in turn led to the development of microcracks and loss of continuity at the grain boundary region and increase in both the grain boundary (major effect) and the lattice (minor effect) resistivity. The behaviour for the grain boundary resistivity after the 800 o C exposure was somewhat similar although expansion of the lattice at 800 o C (or lower temperatures) was considerably less conspicuous. After exposure to H 2-N 2 atmosphere at lower temperatures (650 and 500 o C), although no significant increase in the grain boundary resistivity for exposures up to 1000 hours was observed, the shape of the grain boundary arc was clearly affected. The large increase in the grain boundary resistivity in reduced specimens has been attributed to the observed microcracking, loss of continuity between grains and possibly the formation of new phase regions with extremely poor oxygen-ion conductivity along grain boundaries during the reduction. The disruption to the microstructure is not recovered on subsequent oxidation in air.
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.
Fuel Cells, 2013
ABSTRACT Gadolinia doped ceria thin films are prepared from tetramethylheptanedionate precursors by aerosol assisted chemical vapor deposition, an up-scalable non-vacuum thin film deposition technique. Film growth is studied at substrate temperatures between 300 and 633 °C, and microstructure, cation composition and cross-plane conductivity are assessed. While the total conductivities of gadolinia doped ceria layers deposited at 450 °C are slightly lower than the ionic grain conductivity of Ce0.8Gd0.2O2–d, they are comparable to total conductivities reported for microcrystalline samples in literature. Furthermore, deposition at such low temperatures is promising for processing of thin film assemblies. The preparation of bi-layer electrolytes of yttria stabilized zirconia and gadolinia doped ceria thin films by aerosol assisted chemical vapor deposition is demonstrated. Gadolinia doped ceria films as thin as 150 nm are applied as barrier layers between yttria stabilized zirconia electrolyte and La0.6Sr0.4CoO3–d cathode in anode supported solid oxide fuel cells. High power densities above 850 mW/cm2 at 650 °C are only obtained with these barrier layers, indicating that the GDC thin films effectively inhibit the formation of unwanted interface reactions. Keywords: Ionic Conductivity, Low Temperature SOFC, Novel CVD, Oxide Thin Films, Solid Oxide Fuel Cell
Journal of Electroceramics, 2005
In this study, we report key functional properties of gadolinium-doped ceria (Gd 0.1 Ce 0.9 O 1.95 , GDC) sintered at low temperatures as well as single-cell electrochemical performance of a single-cell prepared there of. GDC solid solutions were sintered at various temperatures ranging 1100-1400 • C and characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), density measurements, mechanical strength tests and electrical conductivity measurements. The dry-pressed GDC disc sample sintered at 1100 • C was found to have 96% of the theoretical density and higher sintering temperatures led to higher densities. SEM micrographs of the fracture and plan surfaces of the sintered discs established the absence of any open pores. The sample sintered at 1100 • C exhibited high electrical conductivity of 0.027 S/cm at 650 • C. The mechanical strength of the sintered samples was determined to be in the range of 150-175 MPa. Greater than 96% of theoretical density, good mechanical strength, and high electrical conductivity of GDC disc samples sintered at 1100 • C established the viability of low-temperature processing of GDC for its use as an SOFC electrolyte. Accordingly, a single-cell was prepared by co-sintering of GDC electrolyte and LSCF-GDC cathode at 1100 • C and subsequent firing of CuO-GDC anode at 900 • C. The electrochemical performance of the cell was evaluated in H 2 fuel at 650 • C.
Low temperature anode-supported solid oxide fuel cells based on gadolinium doped ceria electrolytes
Journal of Power Sources, 2007
The utilization of anode-supported electrolytes is a useful strategy to increase the electrical properties of the solid oxide fuel cells, because it is possible to decrease considerably the thickness of the electrolytes. We have successfully prepared single-chamber fuel cells of gadolinium doped ceria electrolytes Ce 1−x Gd x O 2−y (CGO) supported on an anode formed by a cermet of NiO/CGO. Mixtures of precursor powders of NiO and gadolinium doped ceria with different particle sizes and compositions were analysed to obtain optimal bulk porous anodes to be used as anode-supported fuel cells. Doped ceria electrolytes were prepared by sol-gel related techniques. Then, ceria-based electrolytes were deposited by dip coating at different thicknesses (15-30 m) using an ink prepared with nanometric powders of electrolytes dispersed in a liquid polymer. Cathodes of La 1−x Sr x CoO 3 (LSCO) were also prepared by sol-gel related techniques and were deposited on the electrolyte thick films. Finally, electrical properties were determined in a single-chamber reactor where propane, as fuel, was mixed with synthetic air below the direct combustion limit. Stable density currents were obtained in these experimental conditions. Flux rate values of the carrier gas and propane partial pressure were determinants for the optimization of the electrical properties of the fuel cells.
Transactions of the Materials Research Society of Japan, 2010
Doped ceria (CeO 2) compounds are fluorite related oxides which show oxide ionic conductivity higher than yttria-stabilized zirconia in oxidizing atmosphere. As a consequence of this, considerable interest has been shown in application of these materials for intermediate temperature (300-500C) operation of solid oxide fuel cells (SOFCs). In this review paper, our experimental data was reintroduced to propose a new design paradigm for development of high quality doped CeO 2 electrolytes. Based on our experimental data, our original idea a control of nano-inhomogeity of doped CeO 2 electrolytes was proposed. In our work, the nano-sized powders and dense sintered bodies of M doped CeO 2 (M: Sm, Gd, Y, Yb, Dy, Ho, Tb and La) specimens were fabricated using ammonium carbonate co-precipitation method, conventional sintering method and pulsed electric current sintering method. Also nano-structural features of those specimens were carefully observed for conclusion of relationship between electrolytic properties and microstructure in doped CeO 2. It is essential that the electrolytic properties of doped CeO 2 reflect in changes of microstructure even down to the atomic scale. Accordingly, a combined approach of ultimate analysis, simulation and processing route design is required to develop the superior quality doped CeO 2 electrolytes for the intermediate temperature operation of SOFCs.
Electrolyte materials for solid oxide fuel cells derived from metal complexes: Gadolinia-doped ceria
Ceramics International, 2012
Gadolinia doped ceria (GDC) powders with different gadolinium contents were successfully prepared by the thermal decomposition of ceria complexes. All the calcined powder samples were found to be ceria-based solid-solutions having a fluorite-type structure. The powders were coldisostatically pressed and sintered in air at 1500 8C for 5 h to attain a sintered density of about 90% of its theoretical value. The electrical conductivity of the GDC pellets in air was studied as a function of temperature in the 225-700 8C range, by using two-probe electrochemical impedance spectroscopy measurements. The highest total conductivity (s 600 8C = 0.025 S/cm) was found for the Ce 0.85 Gd 0.15 O 1.925 composition.
Gd3+ and Sm3+ co-doped ceria based electrolytes for intermediate temperature solid oxide fuel cells
Electrochemistry communications, 2004
Co-doped ceria of Ce 1Àa Gd aÀy Sm y O 2À0:5a , wherein a ¼ 0:15 or 0.2, 0 6 y 6 a, were prepared for intermediate temperature solid oxide fuel cells (ITSOFCs). Their structures and ionic conductivities were characterized by X-ray diffraction and AC impedance spectroscopy. All the electrolytes were found to be ceria based solid solutions of fluorite type structures. However, co-doping effect was observed more apparent for the electrolytes with a ¼ 0:15 than for those with a ¼ 0:2. In comparison to the singly doped ceria, the co-doped ceria of Ce 0:85 Gd 0:15Ày Sm y O 1:925 , wherein 0:05 6 y 6 0:1, showed much higher ionic conductivities at 773-973 K. These co-doped ceria are more ideal electrolyte materials of ITSOFCs.
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.
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