| 1. |
- Ma, Ying, 1983-
(författare)
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Ceria-based Nanostructured Materials for Low-Temperature Solid Oxide Fuel Cells
- 2012
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- 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.
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| 2. |
- Wang, Xiaodi, 1981-, et al.
(författare)
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SDC/Na2CO3 nanocomposite : New freeze drying based synthesis and application as electrolyte in low-temperature solid oxide fuel cells
- 2012
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Ingår i: International journal of hydrogen energy. - : Elsevier BV. - 0360-3199 .- 1879-3487. ; 37:24, s. 19380-19387
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 3. |
- Wang, Xiaodi, 1981-, et al.
(författare)
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State of the art ceria-carbonate composites (3C) electrolyte for advanced low temperature ceramic fuel cells (LTCFCs)
- 2012
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Ingår i: International journal of hydrogen energy. - : Elsevier BV. - 0360-3199 .- 1879-3487. ; 37:24, s. 19417-19425
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 4. |
- Wang, Xiaodi, 1981-, et al.
(författare)
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Synthesis of uniform quasi-octahedral CeO2 mesocrystals via a surfactant-free route
- 2011
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Ingår i: Journal of nanoparticle research. - : Springer Science and Business Media LLC. - 1388-0764 .- 1572-896X. ; 13:11, s. 5879-5885
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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