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Ionic Conducting Composite as Electrolyte forLow Temperature Solid Oxide Fuel Cells
KTH, School of Information and Communication Technology (ICT), Material Physics, Functional Materials, FNM. (Functional Materials Division)
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: urn:nbn:se:kth:diva-24723ISBN: 978-91-7415-670-6 (print)OAI: oai:DiVA.org:kth-24723DiVA: diva2:353019
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
List of papers
1. Novel ceramic fuel cell using non-ceria-based composites as electrolyte
Open this publication in new window or tab >>Novel ceramic fuel cell using non-ceria-based composites as electrolyte
2007 (English)In: Electrochemistry communications, ISSN 1388-2481, E-ISSN 1873-1902, Vol. 9, no 12, 2863-2866 p.Article in journal (Refereed) Published
Abstract [en]

A novel concept of ceramic or solid oxide fuel cell (SOFC) based on non-ceria-salt-composites electrolyte has been investigated. The fuel cell using LiAlO2-carbonate (LiNaCO3) as electrolyte exhibits excellent performances, when we used hydrogen and air as fuel and oxidant respectively, instead of molten carbonate fuel cells (MCFCs) environment. The maximum output power density can reach 466 mW/cm(2) at 650 degrees C and the discharging current keeps constant. The ion transport mechanics of the ceramic fuel cell were discussed. In the H-2/air atmosphere, the new fuel cell function should be performed only by proton or oxygen ion conduction, which differs essentially from the MCFC function, in which the CO32- conduction dominates process.

Keyword
LiAlO2, carbonate, non-ceria-based composite electrolytes, fuel cells, low-temperature sofcs, conductors
Identifiers
urn:nbn:se:kth:diva-17177 (URN)10.1016/j.elecom.2007.10.010 (DOI)000251897100025 ()2-s2.0-36248960545 (Scopus ID)
Note
QC 20100525Available from: 2010-08-05 Created: 2010-08-05 Last updated: 2017-12-12Bibliographically approved
2. 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
3. On proton and oxygen co-ion conduction behavior in samarium doped ceria-carbonate nanocomposite electrolyte
Open this publication in new window or tab >>On proton and oxygen co-ion conduction behavior in samarium doped ceria-carbonate nanocomposite electrolyte
Show others...
(English)Article in journal (Other academic) Submitted
Keyword
composite electrolyte, samarium doped ceria (SDC), proton conductivity, oxygen ion conductivity, solid oxide fuel cells (SOFC)
National Category
Materials Engineering
Identifiers
urn:nbn:se:kth:diva-24912 (URN)
Note
QS 20120328Available from: 2010-09-30 Created: 2010-09-30 Last updated: 2012-05-29Bibliographically approved

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