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Thermal stability study of SDC/Na2CO3 nanocomposite electrolyte for low temperatur SOFCs
KTH, School of Information and Communication Technology (ICT), Material Physics, Functional Materials, FNM.
KTH, School of Information and Communication Technology (ICT), Material Physics, Functional Materials, FNM.
KTH, School of Industrial Engineering and Management (ITM), Energy Technology.
KTH, School of Information and Communication Technology (ICT), Material Physics, Functional Materials, FNM.
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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.

Place, publisher, year, edition, pages
2010. Vol. 35, no 7, 2580-2585 p.
Keyword [en]
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: urn:nbn:se:kth:diva-11624DOI: 10.1016/j.ijhydene.2009.03.052ISI: 000276692800002Scopus ID: 2-s2.0-77951022644OAI: oai:DiVA.org:kth-11624DiVA: diva2:278467
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
In thesis
1. Ceria-based nanocomposite electrolyte for low-temperature solid oxide fuel cells
Open this publication in new window or tab >>Ceria-based nanocomposite electrolyte for low-temperature solid oxide fuel cells
2009 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

Solid oxide fuel cells (SOFCs) have attracted much attention because of their potential of providing an efficient, environmentally benign, and fuel-flexible power generation system for both small power units and for large scale power plants. However, conventional SOFCs with yttria-stabilized zirconia (YSZ) electrolyte require high operation temperature (800-1000°C), which presents material degradation problems, as well as other technological complications and economic obstacles. Therefore, numerous efforts have been made to lower the operating temperature of SOFCs. The discovery of new electrolytes for low-temperature SOFCs (LTSOFCs) is a grand challenge for the SOFC community.

 Nanostructured materials have attracted great interest for many different applications, due to their unusual or enhanced properties compared with bulk materials. As an example of enhanced property of nanomaterials, the enhancement of ionic conductivity in the nanostructured solid conductors, known as “nanoionics”, recently become one of the hottest fields of research related to nanomaterials, since they can be used in advanced energy conversion and storage applications, such as SOFC. So in this thesis, we are aiming at developing a novel nanocomposite approach to design and fabricate ceria-based composite electrolytes for LTSOFC. We studied two ceria-based nanocomposite systems with different SDC morphologies.

 In the first part of the thesis, novel core-shell SDC/amorphous Na2CO3 nanocomposite was fabricated 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. The thermal stability of such nanocomposite has also been studied based on careful XRD, BET, SEM and TGA characterization after annealing samples at various temperatures, which indicated that the SDC/Na2CO3 nanocomposite possesses better thermal stability on nanostructure than pure SDC. Such nanocomposite was applied in LTSOFCs with an excellent performance of 0.8 W cm-2 at 550 °C. 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.

In the second part of the thesis, we report a novel chemical synthetic route for the synthesis of samarium doped ceria (SDC) nanowires by homogeneous precipitation of lanthanide citrate complex in aqueous solutions as precursor followed by calcination. The method is template-, surfactant-free and can produce large quantities at low costs. To stabilize these SDC nanowires at high operation temperature, we employed the concept of “nanocomposite” by adding a secondary phase of Na2CO3, as inclusion which effectively hindered the grain growth of nanostructures. The SDC nanowires/Na2CO3 composite was compacted and sintered together with electrode materials, and was then tested for SOFCs performance. It is demonstrated that SOFCs using such SDC nanowires/Na2CO3 composite as electrolyte exhibited better performance compared with state-of-the-art SOFCs using conventional bulk ceria-based materials as electrolytes.

Place, publisher, year, edition, pages
Stockholm: KTH, 2009. vii, 44 p.
Series
Trita-ICT/MAP AVH, ISSN 1653-7610 ; 2009:11
Identifiers
urn:nbn:se:kth:diva-11626 (URN)978-91-7415-497-9 (ISBN)
Presentation
2009-12-04, Sal/Hall E, KTH-Forum, Isafjordsgatan 39, Kista, 10:30 (English)
Opponent
Supervisors
Available from: 2009-11-26 Created: 2009-11-26 Last updated: 2010-10-19Bibliographically approved
2. Ceria-based Nanostructured Materials for Low-Temperature Solid Oxide Fuel Cells
Open this publication in new window or tab >>Ceria-based Nanostructured Materials for Low-Temperature Solid Oxide Fuel Cells
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:nbn:se:kth:diva-95665 (URN)978-91-7501-397-8 (ISBN)
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

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