Preparation and electrical properties of bismuth tungstate solid electrolytes

Solid oxide fuel cells (SOFCs) are high efficiency power generators and operated at high temperature (1000 °C). Consequently, this high operating temperature may lead to many technological problems, such as material durability. Bismuth based electrolytes are able to perform higher ion conductivity t...

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Main Author:	Yuen, Mei Lian
Format:	Thesis
Language:	English
Published:	2016
Subjects:	Bismuth - Electric properties Bismuth compounds Tungstates
Online Access:	http://psasir.upm.edu.my/id/eprint/75457/1/FS%202016%2013%20-%20IR.pdf
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id	my-upm-ir.75457
record_format	uketd_dc
institution	Universiti Putra Malaysia
collection	PSAS Institutional Repository
language	English
topic	Bismuth - Electric properties Bismuth compounds Tungstates
spellingShingle	Bismuth - Electric properties Bismuth compounds Tungstates Yuen, Mei Lian Preparation and electrical properties of bismuth tungstate solid electrolytes
description	Solid oxide fuel cells (SOFCs) are high efficiency power generators and operated at high temperature (1000 °C). Consequently, this high operating temperature may lead to many technological problems, such as material durability. Bismuth based electrolytes are able to perform higher ion conductivity than the current electrolytes (zirconia based) due to its intrinsic property (a quarter of oxygen sites for ions mobility). However, δ-Bi₂O₃ can exhibit high oxide ion conductivity at limited temperature range (730 °C to 825 °C). Introduction of WO₃ into Bi₂O₃ was conducted in an attempt to stabilize δ-Bi₂O₃ down to room temperature. Unfortunately, the produced WO₃ doped Bi₂O₃ materials with a general formula of (1-x)Bi₂O₃-xWO₃, (0.22 ≤ x ≤ 0.255), were unable to stabilize δ-Bi₂O₃. Eventually, these materials synthesized via conventional solid state method and mechanochemical method, respectively, were fully indexed on the tetragonal system with space group I41. Single phase material of Bi6.24W0.88O12, can be obtained at lower temperature with shorter durations through mechanochemical method. The tetragonal structure, Bi6.24W0.88O12, synthesised through mechanochemical method was obtained at 650 °C for 24 hours, while the conventional solid state method synthesized material required a higher temperature (700 °C) for longer duration (48 hours) to obtain a pure phase material. It must be highlighted that Bi6.24W0.88O12 did not undergo decomposition under the studied temperature range (room temperature to 910 °C) based on the XRD patterns from thermal stability experiment and data from thermogravimetric analysis (TGA). This behavior clearly indicated that Bi6.24W0.88O12 was a high stability material. Three vibration bands (ν(W-O-W), Bi-O and ν (W-O)) were noticed in spectra of Fourier-transform infrared (FT-IR) spectroscopy. Scanning Electron Microscopy (SEM) micrographs for pellets sintered at 900 °C illustrated greater grain size compared to pellets sintered at 700 °C. It was inferred that resistance of material could be reduced. X-ray Fluorescence (XRF) analysis recorded data with percentage of error below 5 %, hence, this validated that compositions material and gave a confidence of the current work results. Bi6.24W0.88O12 exhibited the best ionic conductivity among other solid solutions of (1-x)Bi2O3-xWO3, (0.22 ≤ x ≤ 0.255). Bi6.24W0.88O12 fabricated by mechanochemical method demonstrated the highest conductivity of 2.25 x 10-2 ohm-1cm-1 at 600 °C (average grain size of 12.46 μm to 48.16 μm) than conventional solid state route materials. It was also worthwhile to point out that a pure Bi6.24W0.88O12 ion conducting solid electrolyte without any electronic conduction was produced with ionic conductivity of 6 orders higher than the reported YSZ at 600 °C, elucidating a greater potential of Bi6.24W0.88O12 to be used as a material utilized in SOFC electrolytes applications. Doping was carried out on the Bi or W sites in Bi6.24W0.88O12 with selected dopants, including monovalent (Li+), divalent (Ca2+, Cu2+, Ni2+ and Zn2+), trivalent (Cr3+ and Y3+), tetravalent (Sn4+, Ti4+ and Zr4+), pentavalent (Sb5+, V5+, Nb5+ and Ta5+) and hexavalent (Mo6+) cations in order to investigate their effects on the electrical properties of doped Bi6.24W0.88O12 materials. All these dopants can be introduced into Bi6.24W0.88O12 with rather limited solid solution ranges. Ion vacancy, ionic potential and unit cell parameters of structure are the main factors that varying the conductivity of the doped materials. Bi6.24W0.68Nb0.20O11.900 was developed and achieved the highest oxide ion conductivity (2.96 x 10-2 ohm-1cm-1 at 600 °C) among other cation dopants. This doped material was 32 % more conductive than the undoped material. Therefore, it is important to point that this doped material could elevated the performance of SOFC. Nb particles (tiny particle) were homogeneously distributed over the surface ceramic of Bi6.24W0.68Nb0.20O11.900 as illustrated in SEM image.
format	Thesis
qualification_level	Doctorate
author	Yuen, Mei Lian
author_facet	Yuen, Mei Lian
author_sort	Yuen, Mei Lian
title	Preparation and electrical properties of bismuth tungstate solid electrolytes
title_short	Preparation and electrical properties of bismuth tungstate solid electrolytes
title_full	Preparation and electrical properties of bismuth tungstate solid electrolytes
title_fullStr	Preparation and electrical properties of bismuth tungstate solid electrolytes
title_full_unstemmed	Preparation and electrical properties of bismuth tungstate solid electrolytes
title_sort	preparation and electrical properties of bismuth tungstate solid electrolytes
granting_institution	Universiti Putra Malaysia
publishDate	2016
url	http://psasir.upm.edu.my/id/eprint/75457/1/FS%202016%2013%20-%20IR.pdf
_version_	1747813054176821248
spelling	my-upm-ir.754572019-10-18T07:42:34Z Preparation and electrical properties of bismuth tungstate solid electrolytes 2016-02 Yuen, Mei Lian Solid oxide fuel cells (SOFCs) are high efficiency power generators and operated at high temperature (1000 °C). Consequently, this high operating temperature may lead to many technological problems, such as material durability. Bismuth based electrolytes are able to perform higher ion conductivity than the current electrolytes (zirconia based) due to its intrinsic property (a quarter of oxygen sites for ions mobility). However, δ-Bi₂O₃ can exhibit high oxide ion conductivity at limited temperature range (730 °C to 825 °C). Introduction of WO₃ into Bi₂O₃ was conducted in an attempt to stabilize δ-Bi₂O₃ down to room temperature. Unfortunately, the produced WO₃ doped Bi₂O₃ materials with a general formula of (1-x)Bi₂O₃-xWO₃, (0.22 ≤ x ≤ 0.255), were unable to stabilize δ-Bi₂O₃. Eventually, these materials synthesized via conventional solid state method and mechanochemical method, respectively, were fully indexed on the tetragonal system with space group I41. Single phase material of Bi6.24W0.88O12, can be obtained at lower temperature with shorter durations through mechanochemical method. The tetragonal structure, Bi6.24W0.88O12, synthesised through mechanochemical method was obtained at 650 °C for 24 hours, while the conventional solid state method synthesized material required a higher temperature (700 °C) for longer duration (48 hours) to obtain a pure phase material. It must be highlighted that Bi6.24W0.88O12 did not undergo decomposition under the studied temperature range (room temperature to 910 °C) based on the XRD patterns from thermal stability experiment and data from thermogravimetric analysis (TGA). This behavior clearly indicated that Bi6.24W0.88O12 was a high stability material. Three vibration bands (ν(W-O-W), Bi-O and ν (W-O)) were noticed in spectra of Fourier-transform infrared (FT-IR) spectroscopy. Scanning Electron Microscopy (SEM) micrographs for pellets sintered at 900 °C illustrated greater grain size compared to pellets sintered at 700 °C. It was inferred that resistance of material could be reduced. X-ray Fluorescence (XRF) analysis recorded data with percentage of error below 5 %, hence, this validated that compositions material and gave a confidence of the current work results. Bi6.24W0.88O12 exhibited the best ionic conductivity among other solid solutions of (1-x)Bi2O3-xWO3, (0.22 ≤ x ≤ 0.255). Bi6.24W0.88O12 fabricated by mechanochemical method demonstrated the highest conductivity of 2.25 x 10-2 ohm-1cm-1 at 600 °C (average grain size of 12.46 μm to 48.16 μm) than conventional solid state route materials. It was also worthwhile to point out that a pure Bi6.24W0.88O12 ion conducting solid electrolyte without any electronic conduction was produced with ionic conductivity of 6 orders higher than the reported YSZ at 600 °C, elucidating a greater potential of Bi6.24W0.88O12 to be used as a material utilized in SOFC electrolytes applications. Doping was carried out on the Bi or W sites in Bi6.24W0.88O12 with selected dopants, including monovalent (Li+), divalent (Ca2+, Cu2+, Ni2+ and Zn2+), trivalent (Cr3+ and Y3+), tetravalent (Sn4+, Ti4+ and Zr4+), pentavalent (Sb5+, V5+, Nb5+ and Ta5+) and hexavalent (Mo6+) cations in order to investigate their effects on the electrical properties of doped Bi6.24W0.88O12 materials. All these dopants can be introduced into Bi6.24W0.88O12 with rather limited solid solution ranges. Ion vacancy, ionic potential and unit cell parameters of structure are the main factors that varying the conductivity of the doped materials. Bi6.24W0.68Nb0.20O11.900 was developed and achieved the highest oxide ion conductivity (2.96 x 10-2 ohm-1cm-1 at 600 °C) among other cation dopants. This doped material was 32 % more conductive than the undoped material. Therefore, it is important to point that this doped material could elevated the performance of SOFC. Nb particles (tiny particle) were homogeneously distributed over the surface ceramic of Bi6.24W0.68Nb0.20O11.900 as illustrated in SEM image. Bismuth - Electric properties Bismuth compounds Tungstates 2016-02 Thesis http://psasir.upm.edu.my/id/eprint/75457/ http://psasir.upm.edu.my/id/eprint/75457/1/FS%202016%2013%20-%20IR.pdf text en public doctoral Universiti Putra Malaysia Bismuth - Electric properties Bismuth compounds Tungstates

Preparation and electrical properties of bismuth tungstate solid electrolytes

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