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Permanent link (DOI): https://doi.org/10.7939/R3610W31N

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The Investigation of Lanthanum Strontium Chromite (LSC) Based Perovskite Anodes for Solid Oxide Fuel Cells (SOFCs) Open Access

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Other title
Subject/Keyword
SOFCs
anode
perovskite
Type of item
Thesis
Degree grantor
University of Alberta
Author or creator
Sun,Yifei
Supervisor and department
Jing-Li Luo (Chemical and Materials Engineering)
Examining committee member and department
Jing-Li Luo (Chemical and Materials Engineering)
Thomas H. Etsell (Chemical and Materials Engineering)
Steven M. Kuznicki (Chemical and Materials Engineering)
Natalia Semagina (Chemical and Materials Engineering)
Jian Pu (School of Materials Science and Engineering)
Department
Department of Chemical and Materials Engineering
Specialization
Chemical Engineering
Date accepted
2016-05-06T15:35:18Z
Graduation date
2016-06
Degree
Doctor of Philosophy
Degree level
Doctoral
Abstract
Solid oxide fuel cells (SOFC) can be fueled with diverse raw natural gases which usually contain a carbon source and significant amount of H2S. Both of them severely deactivate the Ni-YSZ cermet anode materials and limit their wide applications. Therefore, the potential anode catalysts developed must have excellent coke and sulfur resistances in addition to meeting the general requirements for an anode, including good electrochemical performance as well as chemical stability. The lanthanum chromite perovskite oxide with desirable mechanical and chemical stabilities in redox atmosphere has been regarded as a good interconnection material candidate for SOFCs stack; it is also a suitable and potential anode material for replacing Ni-YSZ. Thorough investigation has shown that its derivative of strontium doped lanthanum chromite (LSC) exhibited higher electrical conductivity. In order to further enhance the catalytic activity of LSC, this study adopted several strategies to fabricate a series of LSC based perovskite oxide anodes and comprehensively investigated their electrochemical and structural properties. A series of Ce-doped La0.7Sr0.3Fe0.5Cr0.5O3–δ (Ce-LSFC) perovskite anode catalysts was firstly synthesized by a modified glycine combustion method. The characterization results illustrate that the pure perovskite structure without formation of CeO2 could be obtained when the content of Ce is ≤ 10%. Compared with the La0.7Sr0.3Fe0.5Cr0.5O3–δ anode, the Ce-LSFC anode not only showed much higher catalytic activity toward the oxidation of syngas with less carbon deposition, but also displayed better regeneration from coking. The enhanced performance was attributed to the more available oxygen vacancies in the lattice and better oxygen mobility after doping with Ce. It is widely known that chemical deposition is one of the most widely used ways to enhance the electrochemical performance of perovskite oxide anodes for SOFCs. However, the anodes produced still have unsatisfactory activity and experience regenerability problems. For the first time, Ni doped LSC perovskite oxides with A-site deficiency (A-LSCNi) were prepared and it was found that the in-situ exsolution of nano Ni could be facilitated after introducing A-site deficiency. The fuel cell with an A-LSCNi anode showed maximum power density of 460 mW/cm2 in 5000 ppm H2S-H2 compared to only 135 mW/cm2 for a fuel cell with a stoichiometric LSCNi anode. Besides, the fuel cell also demonstrates desirable redox stability in sour fuel. The introduction of A-site deficiency can help the formation of highly-mobile oxygen vacancies and remarkably enhance the reducibility of Ni nanoparticles, leading to a significant increase in electronic conductivity and catalytic activity simultaneously. Based on the results mentioned above, the generality of this idea was extended and Ni and Fe doped A-site deficient LaSrCrO3 perovskite (A-LSC) bimetallic anode material was successfully fabricated, on which the exsolution of uniformly dispersed nano Ni-Fe alloy could be in-situ formed in reducing atmosphere. The prepared bimetallic anode catalyst with highly catalytically active nano Ni-Fe alloy exhibited much improved electrochemical performance in sour hydrocarbon fuel (5000 ppm H2S- syngas) and better carbon deposition resistance compared to the monometallic anode catalyst. Furthermore, the application of this type of functional catalyst has been extended to the field of heterogeneous catalysis. For the first time, an iron doped lanthanum strontium chromite with A-site deficiency (A-LSCFe) was fabricated and utilized as an effective bi-functional catalyst for the growth of multiple-walls carbon nanotubes (MWCNTs) and solid oxide fuel cells (SOFCs). The introduction of A-site deficiency significantly facilitates the in-situ exsolution of nano iron particles on which a considerable amount of MWCNTs is grown. The material was also used as the anode catalyst for SOFCs and proved to be a very effective anode catalyst in comparison with the stoichiometric material (sto-LSCFe). The exsolved nano iron particles on A-LSCFe provide many more active sites for the oxidation reaction of the fuel, leading to sharp enhancement of the electrochemical performance of the cell. It was also discovered that the growth of MWCNTs with high electron conductivity leads to a further improvement on the electricity output. The desirable performance and functionality of this series of catalysts offer a bright potential for its promising application in various research fields.
Language
English
DOI
doi:10.7939/R3610W31N
Rights
This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for the purpose of private, scholarly or scientific research. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.
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