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Ceria-based Nanostructured Materials for Low-Temperature Solid Oxide Fuel Cells
KTH, School of Information and Communication Technology (ICT), Material Physics, Functional Materials, FNM.
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

As one of the most efficient and environmentally benign energy conversion devices, solid oxide fuel cells (SOFC) have attracted much attention in recent years. Conventional SOFC with yttria-stabilized zirconia as electrolyte require high operation temperature (800-1000 °C), which causes significant problems like material degradation, as well as other technological complications and economic barrier for wider applications. Therefore, there is a broad interest in reducing the operation temperature of SOFCs. One of the most promising ways to develop low-temperature SOFCs (LTSOFC) is to explore effective materials for each component with improved properties. So in this thesis, we are aiming to design and fabricate ceria-based nanocomposite materials for electrolyte and electrodes of LTSOFC by a novel nanocomposite approach.

In the first part of the thesis, novel core-shell doped ceria/Na2CO3 nanocomposite was fabricated and investigated as electrolytes materials of LTSOFC. Two types of doped ceria were selected as the main phase for nanocomposite: samarium doped ceria (SDC) and calcium doped ceria (CDC). The core-shell SDC/Na2CO3 nanocomposite particles are smaller than 100 nm with amorphous Na2CO3 shell of 4~6 nm in thickness. The ionic conductivity of nanocomposite electrolytes were investigated by EIS and four-probe d.c. method, which demonstrated much enhanced ionic conductivities compared to the single phase oxides. The thermal stability of such nanocomposite has also been investigated based on XRD, BET, SEM and TGA characterization after annealing samples at various temperatures. Such nanocomposite was applied in LTSOFCs with an excellent power density of 0.8 Wcm-2 at 550 °C. The high performances together with notable thermal stability prove the doped ceria/Na2CO3 nanocomposite as a potential electrolyte material for long-term LTSOFCs.

In the second part of the thesis, a novel template-, surfactant-free chemical synthetic route has been successfully developed for the controlled synthesis of hierarchically structured CeO2 with nanowires and mesoporous microspheres morphologies. The new synthetic route was designed by utilizing the chelate formation between cerium ion and various carboxylates forms of citric acid. Then, hierarchically structured cerium oxide with morphologies of nanowires and mesoporous microspheres can be obtained by thermal decomposition of the two kinds of precursors. Moreover, by doping with desired elements, SDC nanowires and SDC-CuO mesoporous microspheres were prepared and used for electrolyte and anode materials, respectively, based on their unique properties depending on their morphologies. When SDC nanowires/Na2CO3 composite were applied as electrolyte for single SOFC, and it exhibited maximum power density of 522 mWcm-2 at 600 °C, which is much better than the state-of-the-art SOFCs using doped ceria as electrolytes. Besides, the mesoporous CuO-SDC composite anode was synthesized by our microwave-assisted method, which shows good phase homogeneity of both SDC and CuO. When it was applied for fuel cells, the cell had better performance than conventional CuO-SDC anode prepared by solid state method.

The whole work of this thesis aims to provide a new methodology for the entire SOFC community. It is notable that our work has attracted considerable attention after publication of several attached papers. The results in this thesis may benefit the development of LTSOFC and expand the related research to a new horizon.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2012. , viii, 42 p.
Series
Trita-ICT/MAP AVH, ISSN 1653-7610 ; 2012:11
National Category
Nano Technology Materials Chemistry
Identifiers
URN: urn:nbn:se:kth:diva-95665ISBN: 978-91-7501-397-8 (print)OAI: oai:DiVA.org:kth-95665DiVA: diva2:528980
Public defence
2012-06-11, Sal- C2, KTH-Electrum, Isafjordsgatan 26, Kista, 10:00 (English)
Opponent
Supervisors
Note
QC 20120530Available from: 2012-05-30 Created: 2012-05-28 Last updated: 2012-05-30Bibliographically approved
List of papers
1. Samarium-doped ceria nanowires: Novel synthesis and application in low-temperature solid oxide fuel cells
Open this publication in new window or tab >>Samarium-doped ceria nanowires: Novel synthesis and application in low-temperature solid oxide fuel cells
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2010 (English)In: Advanced Materials, ISSN 0935-9648, E-ISSN 1521-4095, Vol. 22, no 14, 1640-1644 p.Article in journal (Refereed) Published
Abstract [en]

Samarium-doped ceria (SDC) nanowires are synthesized by a novel, template-, surfactant-free and cost-effective method, using citric acid as precipitating/complexing agent for formation of citrate precursor nanowires. The single SOFC based on SDC nanowires/Na2CO3 nanocomposites as electrolyte is fabricated and the maximum power densities of 417 and 522 mW cm-2 at 550 and 600°C are achieved, showing great potential for low-temperature SOFCs.

Keyword
Chemical equations, Citrate precursor, Cost-effective methods, Low temperatures, Low-temperature solid oxide fuel cells, Maximum power density, Samarium-doped ceria, Surfactant-free
National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-11622 (URN)10.1002/adma.200903402 (DOI)000277205900015 ()2-s2.0-77951149882 (Scopus ID)
Note
QC 20101019. Uppdaterad från Accepted till Published (20101019).Available from: 2009-11-26 Created: 2009-11-26 Last updated: 2017-12-12Bibliographically approved
2. Thermal stability study of SDC/Na2CO3 nanocomposite electrolyte for low temperatur SOFCs
Open this publication in new window or tab >>Thermal stability study of SDC/Na2CO3 nanocomposite electrolyte for low temperatur SOFCs
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2010 (English)In: International journal of hydrogen energy, ISSN 0360-3199, E-ISSN 1879-3487, Vol. 35, no 7, 2580-2585 p.Article in journal (Refereed) Published
Abstract [en]

The novel core-shell nanostructured SDC/Na2CO3 composite has been demonstrated as a promising electrolyte material for low-temperature SOFCs. However, as a nanostructured material, stability might be doubted under elevated temperature due to their high surface energy. So in order to study the thermal stability of SDC/Na2CO3 nanocomposite, XRD, BET, SEM and TGA characterizations were carried on after annealing samples at various temperatures. Crystallite sizes, BET surface areas, and SEM results indicated that the SDC/Na2CO3 nanocomposite possesses better thermal stability on nanostructure than pure SDC till 700 °C. TGA analysis verified that Na2CO3 phase exists steadily in the SDC/Na2CO3 composite. The performance and durability of SOFCs based on SDC/Na2CO3 electrolyte were also investigated. The cell delivered a maximum power density of 0.78 W cm-2 at 550 °C and a steady output of about 0.62 W cm-2 over 12 h operation. The high performances together with notable thermal stability make the SDC/Na2CO3 nanocomposite as a potential electrolyte material for long-term SOFCs that operate at 500-600 °C.

Keyword
BET surface area, CeSmO (SDC), Composite electrolytes, Core-shell, Electrolyte material, Elevated temperature, High surface energy, Low temperatures, Maximum power density, Nano-structured, Nanocomposite electrolytes, SEM, Steady output, Thermal stability, Thermal stability studies, XRD
National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-11624 (URN)10.1016/j.ijhydene.2009.03.052 (DOI)000276692800002 ()2-s2.0-77951022644 (Scopus ID)
Note
QC 20101019. Uppdaterad från In press till Published (20101019).Available from: 2009-11-26 Created: 2009-11-26 Last updated: 2017-12-12Bibliographically approved
3. Enhanced ionic conductivity in calcium doped ceria - Carbonate electrolyte: A composite
Open this publication in new window or tab >>Enhanced ionic conductivity in calcium doped ceria - Carbonate electrolyte: A composite
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2012 (English)In: International journal of hydrogen energy, ISSN 0360-3199, E-ISSN 1879-3487, Vol. 37, no 24, 19401-19406 p.Article in journal (Refereed) Published
Abstract [en]

Recently, ceria-based nanocomposites, as a proton and oxygen ion conductor, has been developed as promising electrolyte candidates for low-temperature solid oxide fuel cells (LTSOFCs). Up to now, samarium doped ceria (SDC) was studied as a main oxide for nanocomposite electrolyte; while calcium doped ceria (CDC) is considered as a good alternative from both material performance and economical aspects. Yet the conduction behavior of CDC-based composite has not been reported. In the present study, calcium doped ceria was prepared by oxalate co-precipitation method, and used for the fabrication of CDC/Na2CO3 composite. The thermal decomposition process, structure and morphology of the samples were characterized by TGA, XRD, SEM, etc. The oxygen ion conductivity of single phase CDC sample was measured by electrochemical impedance spectroscopy (EIS), while the proton and oxygen ion conductivity of CDC/Na2CO3 nanocomposite sample were determined by four-probe d.c. measurements. The CDC/Na2CO3 samples show significantly enhanced overall ionic conductivity compared to that of single phase CDC samples, demonstrating pronounced composite effect. This confirms that the use of nanocomposite as electrolyte can effectively lower the operation temperature of SOFC due to improved ionic conductivity.

Keyword
Nanocomposite electrolyte, Calcium doped ceria (CDC), Proton conductivity, Oxygen ion conductivity, Solid oxide fuel cells (SOFCs)
National Category
Nano Technology
Identifiers
urn:nbn:se:kth:diva-95661 (URN)10.1016/j.ijhydene.2011.09.122 (DOI)000313923900091 ()2-s2.0-84869809752 (Scopus ID)
Funder
Swedish Research CouncilSida - Swedish International Development Cooperation Agency, 2005-6355
Note

QC 20130114

Available from: 2012-05-28 Created: 2012-05-28 Last updated: 2017-12-07Bibliographically approved
4. A surfactant and template-free route for controlled synthesis of hierarchically structured cerium oxides with tunable morphologies and their application for water treatment
Open this publication in new window or tab >>A surfactant and template-free route for controlled synthesis of hierarchically structured cerium oxides with tunable morphologies and their application for water treatment
(English)Article in journal (Other academic) Submitted
National Category
Nano Technology
Identifiers
urn:nbn:se:kth:diva-95663 (URN)
Note
QS 2012Available from: 2012-05-28 Created: 2012-05-28 Last updated: 2012-05-30Bibliographically approved
5. Microwave synthesis of mesoporous CuO-Ce0.8Sm0.2O2-δ composite anode for low-temperature SOFCs
Open this publication in new window or tab >>Microwave synthesis of mesoporous CuO-Ce0.8Sm0.2O2-δ composite anode for low-temperature SOFCs
(English)Article in journal (Other academic) Submitted
National Category
Nano Technology
Identifiers
urn:nbn:se:kth:diva-95664 (URN)
Note
QS 2012Available from: 2012-05-28 Created: 2012-05-28 Last updated: 2012-05-30Bibliographically approved
6. Novel core-shell SDC/amorphous Na2CO3 nanocomposite electrolyte for low-temperature SOFCs
Open this publication in new window or tab >>Novel core-shell SDC/amorphous Na2CO3 nanocomposite electrolyte for low-temperature SOFCs
Show others...
2008 (English)In: Electrochemistry communications, ISSN 1388-2481, E-ISSN 1873-1902, Vol. 10, no 1, 1617-1620 p.Article in journal (Refereed) Published
Abstract [en]

Novel core-shell SDC (Ce0.8Sm0.2O1.9)/amorphous Na2CO3 nanocomposite was prepared for the first time. The core-shell nanocomposite particles are smaller than 100 nm with amorphous Na2CO3 shell of 4-6 nm in thickness. The nanocomposite electrolyte shows superionic conductivity above 300 °C, where the conductivity reaches over 0.1 S cm-1. Such high conductive nanocomposite has been applied in low-temperature solid oxide fuel cells (LTSOFCs) with an excellent performance of 0.8 W cm-2 at 550 °C. A new potential approach of designing and developing superionic conductors for LTSOFCs was presented to develop interface as 'superionic highway' in two-phase materials based on coated SDC.

Keyword
Amorphous, Ce0.8Sm0.2O1.9 (SDC), Composite electrolyte, Core-shell structure, Solid oxide fuel cells (SOFCs)
National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-11625 (URN)10.1016/j.elecom.2008.08.023 (DOI)000260275400053 ()2-s2.0-52149100984 (Scopus ID)
Note
QC 20100924Available from: 2009-11-26 Created: 2009-11-26 Last updated: 2017-12-12Bibliographically approved

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