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Ceria-based nanocomposite electrolyte for low-temperature solid oxide fuel cells
KTH, School of Information and Communication Technology (ICT), Material Physics.
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: urn:nbn:se:kth:diva-11626ISBN: 978-91-7415-497-9 (print)OAI: oai:DiVA.org:kth-11626DiVA: diva2:278472
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
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. 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
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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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