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SDC/Na2CO3 nanocomposite: New freeze drying based synthesis and application as electrolyte in low-temperature solid oxide fuel cells
KTH, School of Information and Communication Technology (ICT), Material Physics (Closed 20120101), Functional Materials, FNM (Closed 20120101). (Functional Materials Division)
KTH, School of Information and Communication Technology (ICT), Material Physics (Closed 20120101), Functional Materials, FNM (Closed 20120101). (Functional Materials Division)
KTH, School of Information and Communication Technology (ICT), Material Physics (Closed 20120101), Functional Materials, FNM (Closed 20120101). (Functional Materials Division)
KTH, School of Industrial Engineering and Management (ITM), Energy Technology.
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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.

Place, publisher, year, edition, pages
2012. Vol. 37, no 24, 19380-19387 p.
Keyword [en]
Nanocomposite, Freeze drying, Proton conduction, Oxygen ion conduction, Solid oxide fuel cells (SOFCs)
National Category
Nano Technology Materials Chemistry
Identifiers
URN: urn:nbn:se:kth:diva-95658DOI: 10.1016/j.ijhydene.2011.10.061ISI: 000313923900088Scopus ID: 2-s2.0-84869817598OAI: oai:DiVA.org:kth-95658DiVA: diva2:528971
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
In thesis
1. 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)
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Note

QC 20120529

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

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