Wet chemical synthesis and physical characterization of doped CeO2 nanoparticles (original) (raw)
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Design of high quality doped CeO2 solid electrolytes with nanohetero structure
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, a considerable interest has been shown in application of these materials for low (400−650°C) temperature operation of solid oxide fuel cells (SOFCs). In this paper, our experimental data about the influence of microstructure at the atomic level on electrochemical properties were reviewed in order to develop high quality doped CeO 2 electrolytes in fuel cell applications. Using this data in the present paper, our original idea for a design of nanodomain structure in doped CeO 2 electrolytes was suggested. The nanosized powders and dense sintered bodies of M doped CeO 2 (M:Sm,Gd,La,Y,Yb, and Dy) compounds were fabricated. Also nanostructural features in these specimens were introduced for conclusion of relationship between electrolytic properties and domain structure in doped CeO 2. It is essential that the electrolytic properties in doped CeO 2 solid electrolytes reflect in changes of microstructure even down to the atomic scale. Accordingly, a combined approach of nanostructure fabrication, electrical measurement and structure characterization was required to develop superior quality doped CeO 2 electrolytes in the fuel cells. Key words doped CeO 2 • oxide ionic conductivity • microdomain • low temperature operation of fuel cells application • nanohetero structure • domain structure
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.
Journal of the American Ceramic Society, 2002
Cation-doped CeO 2 electrolyte has been evaluated in singlecell and short-stack tests in solid oxide fuel cell environments and applications. These results, along with conductivity measurements, indicate that an ionic transference number of ϳ0.75 can be expected at 800°C. Single cells have shown a power density >350 mW/cm 2. Multicell stacks have demonstrated a peak performance of >100 mW/cm 2 at 700°C using metallic separators.
Co-doped ceria-based solid solution in the CeO2–M2O3–CaO, M=Sm, Gd system
Electrochimica Acta, 2010
The Pechinni method (A) as well as hydrothermal treatment (B) of co-precipitated CeO 2-based gels with NaOH solution were used to synthesise pure CeO 2 , and CeO 2-based solid solutions with formula Ce 1−x M x O 2 , Ce 1−x (M 0.5 Ca 0.5) x O 2 M = Gd, Sm for 0.15 < x < 0.3 nanopowders. The thermal evolution of CeO 2based precursors during heating them up to 1000 • C was monitored by thermal (TG, DTA) analysis and X-ray diffraction method. All nanopowders and samples sintered were found to be pure CeO 2 or ceria-based solutions with fluorite-type structure. The microstructure of CeO 2-based sintered samples at 1500 • C (A) or 1250 • C (B) was observed for 2 h under the scanning electron microscope. The electrical properties of singly Ce 1−x M x O 2 or doubly doped CeO 2-based samples with formula Ce 1−x (M 0.5 Ca 0.5) x O 2 , M = Gd, Sm, 0.15 < x < 0.30 were investigated by means of the ac impedance spectroscopy method throughout the temperature range of 600-800 • C. It has been stated that partial substitution of calcium by samarium or calcium by gadolinium in the Ce 1−x (M 0.5 Ca 0.5) x O 2 , M = Gd, Sm solid solutions leads to ionic conductivity enhancement comparable with only samaria-or gadolina-doped ceria. The CeO 2-based samples with small-grained microstructures obtained from powders synthesised by hydrothermal method exhibited better ionic conductivity than samples with the same composition obtained from powders synthesised by the Pechinii method. The stability of the electrolytic properties of selected co-doped ceria sinters in fuel gases (H 2 , CH 4) as well as exhaust gases from diesel engine was also investigated. The codoped Ce 0.8 (Sm 0.5 Ca 0.5) 0.2 O 2 or Ce 0.85 (Gd 0.5 Ca 0.5) 0.15 O 2 dense samples would appear be to more adequate oxide electrolytes than Ce 1−x M x O 2 , M = Sm, Gd and x = 0.15 or 0.2 for electrochemical devices operating at temperatures ranging from 600 to 700 • C.
ECS Transactions, 2013
Samaria doped ceria (SDC) co-doped with Nd 2 O 3 (Nd-SDC) and doubly co-doped with Nd 2 O 3 and Pr 2 O 3 (Pr-Nd-SDC) was prepared by solution combustion synthesis. X-ray diffraction studies confirmed the nanocrystalline nature of the powder with cubic fluorite phase. Raman spectroscopy showed the characteristic cubic fluorite peak (464 cm -1 ) of ceria and the vacancy concentration calculated from the peak area ratio (A 550 /A 464 ) was found to be higher in Pr-Nd-SDC (0.556) compared to Nd-SDC (0.168). The powder was compacted into discs and sintered to obtain dense pellets. The sintering temperature was found to be considerably lower than that required for microcrystalline SDC. The electrical conductivity was obtained by impedance spectroscopy. The doubly co-doped sample (Pr-Nd-SDC) exhibited higher conductivity and lower activation energy compared to the co-doped sample (Nd
2014
Four compositions in the range of 85-90 % CeO 2 , the other being SrO, CaO or Y 2 O 3 combined two or three were studied. The mixtures have been homogenized by a wet route for 10 hours. After drying the obtained powders were subjected to thermal analysis which showed that in the process of grinding chemical changes occur. The apparent and relative densities were measured on the samples sintered at temperatures of 1350 and 1400°C resulting that the relative densities of the samples are between 79 and 92%. X-ray diffraction revealed that the main mineralogical compound of the samples, thermally treated in the range of 1300-1400°C, is a solid solution with a structure of fluorite type specific to CeO 2. For some samples were also identified CaY 4 O 7 and SrCeO 3 , compounds resulting by solid-phase reactions and two solid solutions of the type SrCe 0,85 Y 0,15 O 2,95 and (Ce,Y) 2 O 3 .The microstructure of the studied samples was investigated by electron microscopy and the results showed that the samples exhibit rounded and needle-shaped grains of different sizes. Electrical measurements have shown that three of samples have a corresponding behavior to solid electrolytes usable for IT-SOFC cells. S-au studiat patru compoziţii în care CeO 2 variază de la 85-90%, restul fiind SrO, CaO sau Y 2 O 3 combinaţi câte doi sau trei. Amestecurile au fost omogenizate în mediu umed timp de 10 ore. După uscare pulberile obţinute au fost supuse analizelor termice care au arătat că, în procesul de măcinare, apar modificări chimice. Pe probele sinterizate la temperaturile de 1350 şi 1400 0 C sau determinat densităţile aparente şi relative acestea din urmă, pentru cele patru probe, fiind cuprinse între 79 şi 92%. Componentul mineralogic principal prezent în probele tratate termic în intervalul 1300-1400 0 C, determinat prin difracţie de raze X, este o soluţie solidă cu structură de tipul fluorină specifică CeO 2. În unele probe s-au mai identificat SrCeO 3 şi CaY 4 O 7 compuşi rezultaţi prin reacţii în fază solidă şi două soluţii solide de tipul SrCe 0,85 Y 0,15 O 2,95 şi (Ce,Y) 2 O 3. Textura probelor a fost studiată prin microscopie electronică, probele fiind caracterizate prin granule rotunjite de diferite dimensiuni sau aciculare. Măsurătorile electrice efectuate au arătat că trei dintre probe au o comportare corespunzătoare electroliţilor solizi utilizabili pentru celulele SOFC-IT.
Chemical synthesis of Ca-doped CeO2—Intermediate temperature oxide ion electrolytes
Journal of Power Sources, 2007
Nano-crystalline fluorite-like structure CeO 2 and Ca-doped CeO 2 compounds were prepared in the temperature range of 220-400 • C using a precursor method which involves coprecipitation of Ca 2+ and Ce 4+ ions using oxalic acid from the aqueous calcium chloride and ammonium cerium nitrate solutions. The precipitated products were characterized by employing thermogravimetric analysis (TGA), powder X-ray diffraction (PXRD), infrared spectroscopy (IR), laser particle size analysis (LPSA) methods and scanning electron microscopy (SEM). TGA studies show two step weight loss in the temperature range: (i) room temperature to 200 • C and (ii) 200-400 • C for all the investigated precursors. The former loss is attributed to loss of water while the latter is due to decomposition of oxalates. The XRD study reveal a complex pattern for the as-precipitated powders, and surprisingly we see the formation of single-phase fluorite-like structure at about 220 • C for Ce 1−x Ca x O 2−x (0 < x < 0.20). However, XRD peaks were found to be very broad that sharpen with increasing temperature. The cubic fluorite-type lattice constant increases with increasing Ca-content, which is consistent with literature, and also follows the expected trend based on the ionic radii consideration. For purpose of comparison, Ce 1−x Ca x O 2−x (0 < x < 0.25) samples were also prepared by solid-state reaction using CeO 2 and CaCO 3 , and lattice parameter is consistent with precipitation method samples within the experimental error. This result suggesting that doping of Ca is successful by coprecipitation. The particle size of parent and Ca-doped CeO 2 samples prepared by precipitated method was found to be in the range 10-85 nm (from PXRD) in the temperature range 400-1000 • C, while about order of higher size was observed for the ceramic method synthesized samples. The presently employed wet chemical method could be used to prepare ceria and doped materials with nano-sized particles for a large scale production at mild temperature.
Synthesis of ceria-based nanopowders suitable for manufacturing solid oxide electrolytes
Materials Science-poland, 2008
Co-precipitation method and hydrothermal synthesis were used to fabricate nanopowders of pure CeO 2 and singly or co-doped ceria materials in the CeO 2-Sm 2 O 3-Y 2 O 3 or CeO 2-Gd 2 O 3-Sm 2 O 3 systems. All sintered powders and samples were found to be pure CeO 2 and ceria-based solid solution of fluoritetype structure. The surface areas of CeO 2-based nanopowders were measured by the one-point BET method. The morphologies of powders were observed by means of transmission electron microscopy. Particle sizes of ceria powders synthesised by the hydrothermal method ranged from 9 to 15 nm, the particle sizes of powders calcined at 800 ºC ranged from 13 to 26 nm. The TEM observations indicated that all CeO 2-based powders consisted of isometric in shape and agglomerated particles. Scanning electron microscope was used to observe the microstructure of the sintered samples. Electrical conductivity was studied by the a.c. impedance spectroscopy in the temperature range 200-700 ºC. The oxygen transference number was determined from EMF measurements of oxide galvanic cells. It was found that codoped ceria materials such as Ce 0.8 Sm 0.1 Y 0.1 O 2 or Ce 0.85 Gd 0.1 Sm 0.05 O 2 seem to be more suitable solid electrolytes than singly-doped ceria Ce 1-x M x O 2 (M-Sm, Gd, Y, x = 0.15 or 0.20) for electrochemical devices working in the temperature range 600-700 ºC.
Journal of the Iranian Chemical Society, 2010
The use of alternate cathode materials with improved performance and without any chemical reaction with adjoining electrolyte is required for a reduction in operating temperature of SOFC from 1273 K to about 1073 K (ITSOFC). Cobalt containing perovskite oxides such as LaCoO 3 tend to exhibit a higher ionic conductivity due to a greater concentration of oxygen vacancies than other perovskite oxides. The mixed ionic and electronic conducting cathode of the La 1-x Sr x CoO 3-δ systems has shown the lowest cathodic overpotential for an SOFC air electrode. In this research work, fine powders of La 0.70 Sr 0.30 CoO 3-δ (LSC) cathode and Ce 0.90 Gd 0.10 O 2-δ (GDC) and Ce 0.80 Sm 0.20 O 2-δ (SDC) are synthesized by glycine nitrate combustion synthesis and systematically characterized by XRD and particle characteristics. The electrical properties of LSC cathode and GDC and SDC electrolytes are also studied. But, the crucial requirement for applicability of LSC cathode is its chemical compatibility in conjunction with the alternate solid electrolytes, GDC and SDC without any phase formation. The XRD studies showed no reaction products when the La 0.70 Sr 0.30 CoO 3-δ cathode is mixed and calcined with GDC and SDC electrolyte at 1573 K. Hence, the LSC cathode may be combined with CeO 2 based electrolytes in ITSOFC application.