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Dual-ion Conducting Nanocompoiste for Low Temperature Solid Oxide Fuel Cell
KTH, School of Information and Communication Technology (ICT), Material Physics, Functional Materials, FNM.
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 [en]
Fuel cell, Nano, Composite, Conducting, Electrolyte
National Category
Materials Chemistry Nano Technology
Research subject
SRA - Energy
Identifiers
URN: urn:nbn:se:kth:diva-95652ISBN: 978-91-7501-387-9 (print)OAI: oai:DiVA.org:kth-95652DiVA: diva2:528978
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
List of papers
1. 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
2. SDC/Na2CO3 nanocomposite: New freeze drying based synthesis and application as electrolyte in low-temperature solid oxide fuel cells
Open this publication in new window or tab >>SDC/Na2CO3 nanocomposite: New freeze drying based synthesis and application as electrolyte in low-temperature solid oxide fuel cells
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2012 (English)In: International journal of hydrogen energy, ISSN 0360-3199, E-ISSN 1879-3487, Vol. 37, no 24, 19380-19387 p.Article in journal (Refereed) Published
Abstract [en]

A key issue to develop low-temperature solid oxide fuel cells (LTSOFCs) is to develop new electrolyte materials with enhanced ionic conductivity. Recently, SDC/Na2CO3 nanocomposite, as a proton and oxide co-ion conductor, has been developed as promising electrolyte candidates for LTSOFCs, where Na2CO3 as the secondary phase performs several crucial functions. However, it's difficult to control the homogeneity of Na 2CO3 phase in the composite by the current methods for composite fabrication. In this study, we report a new freeze drying technique to fabricate SDC/Na2CO3 nanocomposites with different content of Na2CO3. Structural and morphological study confirmed that the homogeneity of both SDC and Na2CO3 phases in the nanocomposite is well controlled by the freeze drying technique. The effect of Na2CO3 content on proton and oxygen ion conductivities of SDC-carbonate samples were investigated by the four-probe d.c. measurement. Proton conductivity transformation around 350 °C has been observed for all the SDC/Na2CO3 nanocomposites due to the glass transition of amorphous Na2CO3 phase, and the proton conductivity is dependent on Na2CO3 content. While oxygen ion conductivity deceases with the increasing of Na2CO3 volume fraction in the nanocomposite. Finally, SOFCs were fabricated using SDC/Na2CO3 nanocomposite samples and tested for electrochemical performances. The excellent performance of SOFCs using SDC/Na2CO3 nanocomposite electrolyte verifies that nanocomposite approach is an effective way to fabricate electrolyte with enhanced ionic conductivity for LTSOFCs.

Keyword
Nanocomposite, Freeze drying, Proton conduction, Oxygen ion conduction, Solid oxide fuel cells (SOFCs)
National Category
Nano Technology Materials Chemistry
Identifiers
urn:nbn:se:kth:diva-95658 (URN)10.1016/j.ijhydene.2011.10.061 (DOI)000313923900088 ()2-s2.0-84869817598 (Scopus ID)
Funder
Swedish Research CouncilSida - Swedish International Development Cooperation Agency, 2005-6355
Note

QC 20120529

Available from: 2012-05-28 Created: 2012-05-28 Last updated: 2017-12-07Bibliographically approved
3. State of the art ceria-carbonate composites (3C) electrolyte for advanced low temperature ceramic fuel cells (LTCFCs)
Open this publication in new window or tab >>State of the art ceria-carbonate composites (3C) electrolyte for advanced low temperature ceramic fuel cells (LTCFCs)
2012 (English)In: International journal of hydrogen energy, ISSN 0360-3199, E-ISSN 1879-3487, Vol. 37, no 24, 19417-19425 p.Article in journal (Refereed) Published
Abstract [en]

Solid oxide fuel cells (SOFCs) are considered as one of the most promising power-generation technologies. However, the current high operation temperature (800-1000 °C) of SOFCs impedes their commercialization significantly. A key requirement for reducing the operation temperature of SOFCs is to improve the performance of the electrolyte at such low temperature. Recently, ceria-based composite materials, especially ceria-carbonate composites (3C), have been developed as competitive electrolyte candidates for SOFCs operated below 600 °C, which resulted in an emerging R & D upsurge followed up by worldwide activities. This report gives a short review on current worldwide activities on 3C for advanced low temperature ceramic fuel cells (LTCFCs), which mainly based on recent more than 70 publications since 2010. It gives an overview of materials composition and microstructure, multi-ion conduction effects, durability of the 3C materials in the areas of LTCFC or joint SOFC/MCFC filed, as well as some other novel applications of the 3C materials.

Keyword
Ceria-carbonate composites (3C), Low temperature ceramic fuel cells (LTCFCs), Multi-ion conduction, Solid oxide fuel cells (SOFCs), Molten carbonate fuel cells (MCFC), Interfacial conduction
National Category
Materials Chemistry
Identifiers
urn:nbn:se:kth:diva-95657 (URN)10.1016/j.ijhydene.2011.09.096 (DOI)000313923900093 ()2-s2.0-84869799053 (Scopus ID)
Funder
Vinnova
Note

QC 20120529

Available from: 2012-05-28 Created: 2012-05-28 Last updated: 2017-12-07Bibliographically approved
4. Ceria-based nanocomposite with simultaneous proton and oxygen ion conductivity for low-temperature solid oxide fuel cells
Open this publication in new window or tab >>Ceria-based nanocomposite with simultaneous proton and oxygen ion conductivity for low-temperature solid oxide fuel cells
Show others...
2011 (English)In: Journal of Power Sources, ISSN 0378-7753, E-ISSN 1873-2755, Vol. 196, no 5, 2754-2758 p.Article in journal (Refereed) Published
Abstract [en]

The samarium doped ceria-carbonate (SDC/Na2CO3) nanocomposite systems have shown to be excellent electrolyte materials for low-temperature SOFCs, yet, the conduction mechanism is not well understood. In this study, a four-probe d.c. technique has been successfully employed to study the conduction behavior of proton and oxygen ion in SDC/Na2CO3 nanocomposite electrolyte. The results demonstrated that the SDC/Na2CO3 nanocomposite electrolyte possesses unique simultaneous proton and oxygen ion conduction property, with the proton conductivity 1-2 orders of magnitude higher than the oxygen ion conductivity in the temperature range of 200-600 degrees C, indicating the proton conduction in the nanocomposite mainly accounts for the enhanced total ionic conductivity. It is suggested that the interface in composite electrolyte supplies high conductive path for 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. (C) 2010 Elsevier B.V. All rights reserved.

Keyword
Nanocomposite electrolyte, Samarium doped ceria (SDC), Proton conductivity, Oxygen ion conductivity, Solid oxide fuel cells (SOFCs)
National Category
Inorganic Chemistry
Identifiers
urn:nbn:se:kth:diva-30998 (URN)10.1016/j.jpowsour.2010.11.033 (DOI)000286705100042 ()2-s2.0-78650512018 (Scopus ID)
Funder
Swedish Research Council
Note
QC 20110323Available from: 2011-03-23 Created: 2011-03-07 Last updated: 2017-12-11Bibliographically approved
5. 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
6. Synthesis of uniform quasi-octahedral CeO2 mesocrystals via a surfactant-free route
Open this publication in new window or tab >>Synthesis of uniform quasi-octahedral CeO2 mesocrystals via a surfactant-free route
Show others...
2011 (English)In: Journal of nanoparticle research, ISSN 1388-0764, E-ISSN 1572-896X, Vol. 13, no 11, 5879-5885 p.Article in journal (Refereed) Published
Abstract [en]

A facile surfactant-free nonaqueous method is presented to prepare uniform quasi-octahedral ceria, CeO 2 , mesocrystals, in which only Ce(NO 3 ) 3 and octanol were used as the reactants at a reaction temperature of 150 °C. CeO 2 sample synthesized using this technique consists of well-dispersed quasi-octahedrons and exhibits an uniform size and morphology. Based on structural characterization, it is proposed that the CeO 2 mesostructure was formed by self-assembly of primary nanocrystals based on unique 3D oriented-attachment mechanism. Optical characterization exhibited a strong quantum confinement, revealing small size of primary nanocrystals. The thermal stability and UV–Vis study reveal CeO 2 mesocrystal has various potential for high temperature applications and optical apparatus applications.

National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-50720 (URN)10.1007/s11051-011-0416-x (DOI)000297351600034 ()2-s2.0-84857039371 (Scopus ID)
Note
QC 20111228Available from: 2011-12-07 Created: 2011-12-07 Last updated: 2017-12-08Bibliographically approved

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