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Novel core-shell SDC/amorphous Na2CO3 nanocomposite electrolyte for low-temperature SOFCs
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. KTH, School of Industrial Engineering and Management (ITM), Energy Technology.
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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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.

Place, publisher, year, edition, pages
2008. Vol. 10, no 1, 1617-1620 p.
Keyword [en]
Amorphous, Ce0.8Sm0.2O1.9 (SDC), Composite electrolyte, Core-shell structure, Solid oxide fuel cells (SOFCs)
National Category
Engineering and Technology
Identifiers
URN: urn:nbn:se:kth:diva-11625DOI: 10.1016/j.elecom.2008.08.023ISI: 000260275400053Scopus ID: 2-s2.0-52149100984OAI: oai:DiVA.org:kth-11625DiVA: diva2:278469
Note
QC 20100924Available 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. Ionic Conducting Composite as Electrolyte forLow Temperature Solid Oxide Fuel Cells
Open this publication in new window or tab >>Ionic Conducting Composite as Electrolyte forLow Temperature Solid Oxide Fuel Cells
2010 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

Solid oxide fuel cells (SOFCs) are considered as one of the most promising powergeneration technologies due to their high energy conversion efficiency, fuel flexibilityand reduced pollution. The current SOFCs with yttria-stabilized zirconia (YSZ)electrolyte require high operation temperature (800-1000 °C), which not only hinderstheir broad commercialization due to associated high cost and technologicalcomplications. Therefore, there is a broad interest in reducing the operating temperatureof SOFCs. The key to development of low-temperature SOFCs (LTSOFCs) is to explorenew electrolyte materials with high ionic conductivity at such low temperature (300-600 °C).Recently, ceria-based composite electrolyte, consisting of doped cerium oxide mixedwith a second phase (e.g. Na2CO3), has been investigated as a promising electrolyte forLTSOFCs. The ceria-based composite electrolyte has shown a high ionic conductivityand improved fuel cell performance below 600 °C. However, at present the developmentof composite electrolyte materials and their application in LTSOFCs are still at an initialstage. This thesis aims at exploring new composite systems for LTSOFCs with superiorproperties, and investigates conductivity behavior of the electrolyte. Two compositesystems for SOFCs have been studied in the thesis.In the first system, a novel concept of non-ceria-salt-composites electrolyte, LiAlO2-carbonate (Li2CO3-Na2CO3) composite electrolyte, was investigated for SOFCs. TheLiAlO2-carbonate electrolyte exhibited good conductivity and excellent fuel cellperformances below 650 oC. The ion transport mechanism of the LiAlO2-carbonatecomposite electrolyte was studied. The results indicated that the high ionic conductivityrelates to the interface effect between oxide and carbonate.In the second system, we reported a novel core-shell samarium-doped ceria(SDC)/Na2CO3 nanocomposite which is proposed for the first time, since the interface isdominant in the nanostructured composite materials. The core-shell nanocompositeparticles are smaller than 100 nm with amorphous Na2CO3 shell. The nanocompositeelectrolyte was applied in LTSOFCs and showed excellent performance. Theconductivity behavior and charge carriers have been studied. The results indicated that H+conductivity in SDC/Na2CO3 nanocomposite is predominant over O2- conductivity with1-2 orders of magnitude in the temperature range of 200-600 °C. It is suggested that theinterface in composite electrolyte supplies high conductive path for proton, while oxygenions are most probably transported by the SDC nano grain interiors. Finally, a tentativemodel “swing mechanism” was proposed for explanation of superior proton conduction.

Place, publisher, year, edition, pages
Royal institute of technology, 2010. 43 p.
Series
Trita-ICT/MAP AVH, ISSN 1653-7610 ; 2010:05
Identifiers
urn:nbn:se:kth:diva-24723 (URN)978-91-7415-670-6 (ISBN)
Presentation
2010-06-07, Electrum C2, Isajordsgatan 23, Kista, Stockholm, 16:27 (English)
Opponent
Supervisors
Note
QC 20100930Available from: 2010-09-30 Created: 2010-09-23 Last updated: 2010-09-30Bibliographically approved
3. Dual-ion Conducting Nanocompoiste for Low Temperature Solid Oxide Fuel Cell
Open this publication in new window or tab >>Dual-ion Conducting Nanocompoiste for Low Temperature Solid Oxide Fuel Cell
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Solid oxide fuel cells (SOFCs) are considered as one of the most promising power generation technologies due to their high energy conversion efficiency, fuel flexibility and reduced pollution. There is a broad interest in reducing the operating temperature of SOFCs. The key issue to develop low-temperature (300~600 °C) SOFCs (LTSOFCs) is to explore new electrolyte materials. Recently, ceria-based composite electrolytes have been developed as capable alternative electrolyte for LTSOFCs. The ceria-based composite electrolyte has displayed high ionic conductivity and excellent fuel cell performance below 600 °C, which has opened up a new horizon in the LTSOFCs field. In this thesis, we are aiming at exploring nanostructured composite materials for LTSOFCs with superior properties, investigating the detailed conduction mechanism for their enhanced ionic conductivity, and extending more suitable composite system and nanostructure materials.In the first part, core-shell samarium doped ceria-carbonate nanocomposite (SDC/Na2CO3) was synthesized for the first time. The core-shell nanocomposite was composed of SDC particles smaller than 100 nm coated with amorphous Na2CO3 shell. The nanocomposite has been applied in LTSOFCs with excellent performance. A freeze dry method was used to prepare the SDC/Na2CO3 nanocomposites, aiming to further enhance its phase homogeneity. The ionic conduction behavior of the SDC/Na2CO3 nanocomposite has been studied. The results indicated that H+ conductivity in the nanocomposite is predominant over O2- conductivity with 1-2 orders of magnitude in the temperature range of 200-600 °C, indicating the proton conduction in the nanocomposite mainly accounts for the enhanced total ionic conductivity. The influence of Na2CO3 content to the proton and oxygen ion conductivity in the nanocomposite was studied as well.In the second part, both the proton and oxygen ion conduction mechanisms have been studied. It is suggested that the interface in the nanocomposite electrolyte supplies high conductive path for the proton, while oxygen ions are probably transported by the SDC grain interiors. An empirical “Swing Model” has been proposed as a possible mechanism of superior proton conduction, while oxygen ion conduction is attributed to oxygen vacancies through SDC grain in nanocomposite electrolyte.In the final part, a novel concept of non-ceria-salt-composites electrolyte, LiAlO2-carbonate composite electrolyte, has been investigated for LTSOFCs. The LiAlO2-carbonate electrolyte exhibits good conductivity and excellent fuel cell performances below 650 °C. The work not only developed a more stable composite material, but also strongly demonstrated that the high ionic conductivity is mainly related to interface effect between oxide and carbonate. As a potential candidate for nanocomposite, uniform quasi-octahedral CeO2 mesocrystals was synthesized in this thesis work as well. The CeO2 mesocrystals shows excellent thermal stability, and display potential for fuel cell applications.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2012. ix, 58 p.
Series
Trita-ICT/MAP AVH, ISSN 1653-7610 ; 2012:10
Keyword
Fuel cell, Nano, Composite, Conducting, Electrolyte
National Category
Materials Chemistry Nano Technology
Research subject
SRA - Energy
Identifiers
urn:nbn:se:kth:diva-95652 (URN)978-91-7501-387-9 (ISBN)
Public defence
2012-06-07, Sal C2, KTH-Electrum, Isafjordsgatan 26,, Kista, 10:00 (English)
Opponent
Supervisors
Funder
StandUp
Note

QC 20120529

Available from: 2012-05-29 Created: 2012-05-28 Last updated: 2013-04-18Bibliographically approved
4. 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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