Enhanced chemical stability and sinterability of refined proton-conducting perovskite: Case study of BaCe0.5Zr0.3Y0.2O3−δ (original) (raw)
Journal of The Electrochemical Society, 2010
The chemical stability and electrical properties of three promising perovskite-related structures BaCe 0.8 Gd 0.15 Pr 0.05 O 3−␦ , BaCe 0.85 Sm 0.15 O 3−␦ , and BaCe 0.85 Eu 0.15 O 3−␦ were tested in air, humidified N 2 and H 2 , as well as in D 2 O + N 2. Powder X-ray diffraction studies confirmed the formation of a cubic perovskite-like structure. The change in the lattice constant was consistent with B-site substitution in BaCeO 3. All the investigated compounds formed barium carbonate in CO 2 at elevated temperatures and were found to be chemically unstable in boiling H 2 O. The data showed that these three compounds are chemically stable in humidified CH 4 at 800°C; however, at 600°C, the formation of barium carbonate was observed. The electrical conductivity in wet N 2 and/or H 2 was found to be higher than that in the D 2 O-containing atmosphere, confirming proton conduction in the doped BaCeO 3. The Gd + Pr co-doped BaCeO 3 showed the highest total conductivity of 2.58 ϫ 10 −2 S cm −1 in H 2 + 3% H 2 O at 700°C with an activation energy of 0.36 eV in the temperature range of 450-700°C.
Rare-earth-doped BaCeO 3 and BaZrO 3 electrolytes with perovskite structure have been studied extensively in developing intermediate temperature SOFC. Traditional solid state sintering has been used to prepare the perovskite type proton conductors Ba(Ce,Zr) 1−x Sc x O 3 − δ (x = 0.1, 0.2). Rietveld refinement of the XRD data shows the materials as cubic in the space group Pm-3m. The unit cell parameter a decreases with Sc concentration. Thermogravimetric analysis (TGA) traces obtained for dehydrated samples on heating in a 3% H 2 O/5% H 2 /Ar atmosphere show that, on heating, initially the sample weight remains constant up to 400°C and then decreases. TGA in pure CO 2 shows that Sc doping increases the chemical stability. AC impedance measurements under wet 5% H 2 /Ar show that these materials are good conductors and stable under H 2 atmosphere. It also shows that bulk and grain boundary resistances decrease with Sc doping. The total conductivity increases from 2.58 × 10 − 4 Scm − 1 to 1.06 × 10 − 3 Scm − 1 for x = 0.1 and 0.2 respectively at 600°C.
Diffusion and Defect Data Pt.B: Solid State Phenomena, 2011
From neutron diffraction it is known that the BaCeO 3 perovskite undergoes a sequence of phase transformations from high temperature cubic C to rhombohedral R, to orthorhombic O1 (Imma) and to orthorhombic O2 (Pnma). Doping Y 3+ on the Ce 4+ site introduces charge compensating O vacancies (V O ) that may be partially filled with OH complexes with exposition to H 2 O, so making the material an ionic conductor.
Inorganic Chemistry, 2011
We report the effect of donor-doped perovskitetype BaCeO 3 on the chemical stability in CO 2 and boiling H 2 O and electrical transport properties in various gas atmospheres that include ambient air, N 2 , H 2 , and wet and dry H 2 . Formation of perovskite-like BaCe 1Àx Nb x O 3(δ and BaCe 0.9Àx Zr x Nb 0.1 O 3(δ (x = 0.1; 0.2) was confirmed using powder X-ray diffraction (XRD) and electron diffraction (ED). The lattice constant was found to decrease with increasing Nb in BaCe 1Àx Nb x O 3(δ , which is consistent with Shannon's ionic radius trend. Like BaCeO 3 , BaCe 1Àx Nb x O 3(δ was found to be chemically unstable in 50% CO 2 at 700°C, while Zr doping for Ce improves the structural stability of BaCe 1Àx Nb x O 3(δ . AC impedance spectroscopy was used to estimate electrical conductivity, and it was found to vary with the atmospheric conditions and showed mixed ionic and electronic conduction in H 2 -containing atmosphere. Arrhenius-like behavior was observed for BaCe 0.9Àx Zr x Nb 0.1 O 3(δ at 400À700°C, while Zr-free BaCe 1Àx Nb x O 3(δ exhibits non-Arrhenius behavior at the same temperature range. Among the perovskite-type oxides investigated in the present work, BaCe 0.8 Zr 0.1 Nb 0.1 O 3(δ showed the highest bulk electrical conductivity of 1.3 Â 10 À3 S cm À1 in wet H 2 at 500°C, which is comparable to CO 2 and H 2 O unstable high-temperature Y-doped BaCeO 3 proton conductors.
Properties of Perovskite-Type Proton Conductors
2013
Investigations of perovskite-type BaCeO3 and SrCeO2 with various dopants (Y, Gd, Nd, and Ni) indicate that their microstructures and electrical properties are strongly influenced by the type and amount of dopants. Grain growth and densification of sintered samples are influenced by dopant level and A:B site nonstoichiometry. The conductivity of BaCe1_Y039 increases with the yttrium content in hydrogen and wet Ar; and exhibits a maximum in oxygen at an yttrium content of 10 to 20%. BaCe08Y0203_1 has the highest conductivity in a hydrogen atmosphere:-4.54 X 10-2 11' cm' at 600°C, and-4.16 >< 10 fl1 cm1 at 800°C. The effect of BaO excess depends on the concentration of dopant. Compared with BaCe091Y01503_0, doped BaCeO3 with BaO excess (Ba00.90Ce020.025Y203) has a higher total conductivity in all atmospheres studied (02, H2, and wet Ar), whereas the conductivity of BaCeO3 with excess BaO (Ba00.85Ce020.05Y203) is lower than that of BaCe09Y61O26. BaCeO3 based materials have higher conductivities than those of SrCeO2 based materials, whereas SrCeO3 based materials show higher proton transference numbers.
Journal of Materials Chemistry, 2008
High-temperature proton conductors are promising as electrolytes for intermediate-temperature solid oxide fuel cells. Among them, BaCeO 3 -based materials have high proton conductivity but rather poor chemical stability. In contrast, barium zirconates are rather stable, but have poorly reproducible densities and conductivities. In this study, the investigation of BaCe 1ÀxÀy Zr x Y y O 3Àd solid solutions (x ¼ 0, 0.10, 0.20, 0.30, 0.40; y ¼ 0.15, 0.20) was undertaken, with the final aim of finding a composition having both high conductivity and good stability. The influence of the modified sol-gel Pechini synthetic approach on the powder morphology, and of a barium excess on the densification were demonstrated. Single-phase perovskite powders were prepared and high density pellets were obtained at temperatures lower than those commonly employed. Stability tests demonstrated that the Zr introduction into doped barium cerate greatly enhanced the chemical stability, particularly for Zr $ 20%. The proton conductivities, measured in a humidified H 2 /Ar atmosphere by impedance spectroscopy, were only slightly influenced by the Zr amount. Overall, BaCe 1ÀxÀy Zr x Y y O 3Àd solid solutions having Zr z 20-40% and Y z 15-20% showed good chemical stability and high conductivity.
Materials Research Bulletin, 2010
The influence of barium content on the structural characteristics, sinterability and electrical conductivity of proton conductor Ba x Ce 0.50 Zr 0.40 Y 0.10 O 3Àd (x = 0.95, 0.97, 1.00, 1.03, 1.05) is investigated. Compositions with barium deficiency show the presence of fluorite precipitate detected by powder X-ray diffraction, whilst pure perovskite phase is present for other samples. Barium deficiency promotes the densification process of the samples. The electrical conductivity of Ba x Ce 0.50 Zr 0.40 Y 0.10 O 3Àd increases with barium content, which is mainly ascribed to the decreased activation energy due to the increasing lattice volume, especially for the case in wet 5% H 2 /Ar. The present results suggest that it is very important to control the stoichiometry of cations to obtain desirable perovskite type high temperature proton conductors. ß
ACS Applied Energy Materials, 2020
Oxides with proton conductivity have a great potential for applications in environmental energy technology. Despite the Ba-Ce 0.4 Zr 0.4 Y 0.2 O 3-δ (BCZY) perovskites being well-known proton conductors, it is a challenge to determine the optimal operating temperature range where the energy applications benefit most from this unique property. The protonic transport properties strongly depend on crystal structure and local distortions in the participating cation coordination sphere, according to related temperatures and gas feed. The transport and crystallographic properties of BCZY were simultaneously studied by impedance spectroscopy (IS) and synchrotron X-ray diffraction (S-XRD). A strong correlation between conductivity and the lattice parameter, corresponding in principle to a cubic symmetry, was observed, mainly between 400 and 700 °C. The protonic conductivity range was analyzed by the H/D isotopic effect on the impedance spectra, which helped to identify protonic conduction as the governing transport mechanism below 600 °C, while the transport via oxygen vacancies dominates above this temperature. In order to assess the real crystallographic structure, the simultaneous refinement of laboratory XRD and neutron diffraction (ND) patterns was performed. According to this, BCZY changes from rhombohedral symmetry below 400 °C to cubic at 600 °C in a second-order phase transition. Complementary quasielastic neutron scattering (QENS) enables us to determine a protonic jump length of 3.1 Å, which matches the O-O distances in the octahedral oxygen coordination sphere around the cations. These results support the protonic self-diffusion through proton hopping between intraoctahedral O sites as the main transport mechanism up to 600 °C.
2010
The sinterability, conductivity and chemical stability in CO2 atmosphere are compared for a series of doped barium cerate perovskite oxides BaCe0.7Zr0.1Y0.2-xNdxO3- (0 ≤ x ≤ 0.2) which synthesized using a solid state reaction method. Among the series of electrolytes doped with various amounts of Nd and Y, BaCe0.7Zr0.1Y0.15Nd0.05O3- has the optimal combination of sinterability and conductivity, and shows high CO2 resistance. A solid oxide fuel cell using the BaCe0.7Zr0.1Y0.15Nd0.05O3- proton conducting electrolyte at 650-700 o C efficiently co-produces electrical power and value-added ethylene from ethane.
Acceptor-doped BaCeO 3 perovskites have frequently been studied as high temperature proton conductors (HTPCs) where conduction occurs due to hydroxyl protons that occupy the oxide ion vacancies in the perovskite-type structure. Recently, donor-doped perovskites of the nominal composition BaCe 0.7 Zr 0.2 Nb 0.1 O 3 have demonstrated mixed proton-electron conduction in humidified H 2 and N 2. The proton conduction mechanism is assumed to be similar to that of acceptor-doped perovskites, where the reduction of B-site cations is suggested. In this study, BaCe 1À(x+y) Zr x Nb y O 3 (x ¼ 0.05-0.2, y ¼ 0.05-0.1) are characterized using X-ray photoelectron spectroscopy (XPS), powder X-ray diffraction (PXRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), and AC impedance spectroscopy. The role of composition and sintering temperature on microstructural, chemical, stoichiometric, and electrical properties is thoroughly investigated. PXRD shows the formation of orthorhombic perovskites in all samples and SEM images reveal that a decrease in porosity and increase in grain size are significantly affected by relative Zr and Nb dopant levels. The improved densification caused by the Nb doping leads to enhanced total conductivity by lowering the grain-boundary resistance. Surface analysis by XPS indicates that Ba vacancies in as-prepared BaCe 1À(x+y) Zr x Nb y O 3 can be controlled by composition and temperature control. The co-doping of Nb and Zr lead to enhanced chemical stability in CO 2 at elevated temperatures compared to the parent compound. The bulk electrical conductivity decreases with increasing Zr content in BaCe 1À(x+y) Zr x Nb y O 3 in air. Among the samples investigated in this work, BaCe 0.9 Zr 0.05 Nb 0.05 O 3 exhibits the highest bulk conductivity of 10 À3 S cm À1 at 400 C with an activation energy of 0.43 eV (400-700 C).