Studies on Chemical Stability and Electrical Properties of Proton Conducting Perovskite-Like Doped BaCeO[sub 3] (original) (raw)
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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.
Investigation of the protonic conduction in Sm doped BaCeO3
Journal of Power Sources, 2008
In the present work the structural and electrical properties of samarium-doped barium cerate perovskites of BaCe 1−x Sm x O 3−␦ formula (with x = 0-0.2), prepared by following the solid state reaction method, are investigated. The crystal structure and microstructure of the samples is determined by employing the techniques of X-ray Diffraction (XRD) and Scanning Electron Microscopy (SEM). According to the XRD analysis at 0 ≤ x ≤ 0.2 the formed continuous series of BaCe 1−x Sm x O 3−δ solid solutions have the structure of cubic perovskite with orthorhombic distortions. It was found that the relative density of the samples is ∼87% for 0.02 < x < 0.05 and ∼94% for 0.05 < x < 0.25. It was also found that the highest conductivity is observed for x = 0.15. Finally, the thermal expansion of BaCe 1−x Sm x O 3−δ (x = 0-0.2) is studied and the thermal expansion coefficients for the high temperature region are calculated. Published by Elsevier B.V.
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).
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.
Materials Chemistry and Physics, 2018
Current industrialization era stresses upon taking intensive measures to recognize and utilize sustainable, eco-friendly and high energy output generating resources, thus, shifting focus towards proton conducting fuel cells (PCFCs) for use in industrial, residential and transportation sectors. Accordingly, the following research focused on the development of a novel gadoliniumdoped electrolyte material i.e. BaCe0.59Zr0.2Y0.15Gd0.06O2.97-δ (BCZYG59) for PCFCs using solid-state and wet-chemical synthesis approach. X-ray Diffraction Analysis (XRD) and Scanning Electron Microscopy (SEM) were carried out for analyzing microstructural morphology, grain-growth and characteristics, densification trends and other phase/structural transformations, whereas, electrical properties were investigated via DC conductivity testing to examine BCZYG59's feasibility as electrolyte. Homogenous cubic perovskite phase for ensuring proton conduction was achieved at 1300⁰C and 1500⁰C for BCZYG59 synthesized from wetchemical and solid-state methods, respectively. These materials showed corresponding conductivity values of 3.20×10-4 S.cm-1 and 4.70×10-4 S.cm-1 at 650⁰C in air with the promising prospects of exhibiting greater proton conductivity making it a fairly convincing choice among present-day electrolyte materials.
Synthesis, Structure and Proton Conduction of Substituted BaTiO3 and BaZrO3 Perovskites
2013
Proton conducting oxides can be beneficial as electrolyte materials in devices such as fuel cells, hydrogen sensors etc. Proton conducting fuel cells (PCFCs), utilising H 2 as fuel, stand out as a promising technology for future clean energy generation. The works herein is devoted to improve the performance of current state of the art perovskite structured BaZrO 3 based electrolyte materials as well as synthesise and characterise novel electrolytes within the BaTiO 3 based systems. Usually acceptor doping of these perovskites allows for proton conductivity in hydrogen containing atmosphere. In this thesis heavily co-doped strategy along with the impact of addition of sintering aid (ZnO) and various synthesis routes in BaZrO 3 based materials is being tested. Heavily doped BaTiO 3 based systems are also synthesised for the first time and characterised with an emphasis on proton conduction. This work is based on techniques such as X-ray powder diffraction studies, neutron powder diffraction, thermogravimetric analysis and AC impedance spectroscopy. In addition a neutron total scattering study is employed for the first time to understand the local structural environment for the deuteron position in a proton conducting electrolyte. Co-doping and sintering aid (in solution synthesis) for the In/Yb:BaZrO 3 electrolyte seems to be beneficial. Heavily substituted Sc/In:BaTiO 3 materials also show enhanced proton conductivity.
Chemically stable proton conducting doped BaCeO₃ -no more fear to SOFC wastes
Scientific reports, 2013
Development of chemically stable proton conductors for solid oxide fuel cells (SOFCs) will solve several issues, including cost associated with expensive inter-connectors, and long-term durability. Best known Y-doped BaCeO3 (YBC) proton conductors-based SOFCs suffer from chemical stability under SOFC by-products including CO2 and H2O. Here, for the first time, we report novel perovskite-type Ba0.5Sr0.5Ce0.6Zr0.2Gd0.1Y0.1O3-δ by substituting Sr for Ba and co-substituting Gd + Zr for Ce in YBC that showed excellent chemical stability under SOFC by-products (e.g., CO2 and H2O) and retained a high proton conductivity, key properties which were lacking since the discovery of YBCs. In situ and ex- situ powder X-ray diffraction and thermo-gravimetric analysis demonstrate superior structural stability of investigated perovskite under SOFC by-products. The electrical measurements reveal pure proton conductivity, as confirmed by an open circuit potential of 1.15 V for H2-air cell at 700°C, an...
Journal of Power Sources, 2009
In this paper, we report the synthesis, chemical stability and electrical properties of three new Tasubstituted double perovskite-type Ba 2 Ca 2/3 Nb 4/3 O 6 (BCN). The powder X-ray diffraction (PXRD) confirms the formation of double perovskite-like structure Ba 2 (Ca 0.75 Nb 0.59 Ta 0.66 )O 6−ı , Ba 2 (Ca 0.75 Nb 0.66 Ta 0.59 )O 6−ı and Ba 2 (Ca 0.79 Nb 0.66 Ta 0.55 )O 6−ı . The PXRD of CO 2 treated (800 • C; 7 days) and water boiled (7 days) samples remain the same as the as-prepared samples, suggesting a long-term structural stability against the chemical reaction. The electrical conductivity of the investigated perovskites was found to vary in different atmospheres (air, dry N 2 , wet N 2 , H 2 and D 2 O + N 2 ). The AC impedance investigations show bulk, grain-boundary and electrode contributions in the frequency range of 0.01 Hz to 7 MHz. Below 600 • C, the bulk conductivity in wet H 2 and wet N 2 was higher than in air, dry H 2 and dry N 2 . However, an opposite trend was observed at high temperatures, which may be ascribed to p-type electronic conduction. The electrical conductivity of the investigated perovskites was decreased in D 2 O + N 2 compared to that of H 2 O + N 2 atmosphere. This clearly shows that the investigated Ta-doped BCN compounds exhibit proton conduction in wet atmosphere which was found to be consistent with water uptake. The water uptake was further confirmed by thermogravimetric analysis (TGA) and Fourier transform infrared spectroscopy (FTIR) characterization. Among the samples investigated, Ba 2 (Ca 0.79 Nb 0.66 Ta 0.55 )O 6−ı shows the highest proton conductivity of 4.8 × 10 −4 S cm −1 (at 1 MHz) at 400 • C in wet (3% H 2 O) N 2 or H 2 , which is about an order of magnitude higher than the recently reported 1% Ca-doped LaNbO 4 at the same atmosphere and at 10 kHz.
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.