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Advanced BaZrO3-BaCeO3 Based Proton Conductors Used for Intermediate Temperature Solid Oxide Fuel Cells (ITSOFCs)
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Process Metallurgy.ORCID iD: 0000-0001-5258-099X
2015 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

In this thesis, the focus is on studying BaZrO3-BaCeO3 based proton conductors due to that they represent very promising proton conductors to be used for Intermediate Temperature Solid Oxide Fuel Cells (ITSOFCs). Here, dense BaZr0.5Ce0.3Y0.2O3-δ (BZCY532) ceramics were selected as the major studied materials. These ceramics were prepared by different sintering methods and doping strategies. Based on achieved results, the thesis work can simply be divided into the following parts:

1) An improved synthesis method, which included a water-based milling procedure followed by a freeze-drying post-processing, was presented. A lowered calcination and sintering temperature for a Hf0.7Y0.3O2-δ (YSH) compound was achieved. The value of the relative density in this work was higher than previously reported data. It is also concluded that this improved method can be used for mass-production of ceramics.

2) As the solid-state reactive sintering (SSRS) represent a cost-effective sintering method, the sintering behaviors of proton conductors BaZrxCe0.8-xLn0.2O3-δ (x = 0.8, 0.5, 0.1; Ln = Y, Sm, Gd, Dy) during the SSRS process were investigated. According to the obtained results, it was found that the sintering temperature will decrease, when the Ce content increases from 0 (BZCLn802) to 0.3 (BZCLn532) and 0.7 (BZCLn172). Moreover, the radii of the dopant ions similar to the radii of Zr4+ or Ce4+ ions show a better sinterability. This means that it is possible to obtain dense ceramics at a lower temperature. Moreover, the conductivities of dense BZCLn532 ceramics were determined. The conductivity data indicate that dense BZCY532 ceramics are good candidates as either oxygen ion conductors or proton conductors used for ITSOFCs.

3) The effect of NiO on the sintering behaviors, morphologies and conductivities of BZCY532 based electrolytes were systematically investigated. According to the achieved results, it can be concluded that the dense BZCY532B ceramics (NiO was added during ball-milling before a powder mixture calcination) show an enhanced oxygen and proton conductivity. Also, that BZCY532A (NiO was added after a powder mixture calcination) and BZCY532N (No NiO was added in the whole preparation procedures) showed lower values. In addition, dense BZCY532B and BZCY532N ceramics showed only small electronic conductivities, when the testing temperature was lower than 800 ℃. However, the BZCY532A ceramics revealed an obvious electronic conduction, when they were tested in the range of 600 ℃ to 800 ℃. Therefore, it is preferable to add the NiO powder during the BZCY532 powder preparation, which can lower the sintering temperature and also increase the conductivity.

4) Dense BZCY532 ceramics were successfully prepared by using the Spark Plasma Sintering (SPS) method at a temperature of 1350 ℃ with a holding time of 5 min. It was found that a lower sintering temperature (< 1400 ℃) and a very fast cooling rate (> 200 ℃/min) are two key parameters to prepare dense BZCY532 ceramics. These results confirm that the SPS technique represents a feasible and cost-effective sintering method to prepare dense Ce-containing BaZrO3-BaCeO3 based proton conductors.

5) Finally, a preliminary study for preparation of Ce0.8Sm0.2O2-δ (SDC) and BZCY532 basedcomposite electrolytes was carried out. The novel SDC-BZCY532 based composite electrolytes were prepared by using the powder mixing and co-sintering method. The sintering behaviors, morphologies and ionic conductivities of the composite electrolytes were investigated. The obtained results show that the composite electrolyte with a composition of 60SDC-40BZCY532 has the highest conductivity. In contrast, the composite electrolyte with a composition of 40SDC-60BZCY532 shows the lowest conductivity.

In summary, the results show that BaZrO3-BaCeO3 based proton-conducting ceramic materials represent very promising materials for future ITSOFCs electrolyte applications.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2015. , x, 66 p.
Keyword [en]
Solid oxide fuel cells (SOFCs); Intermediate temperature solid oxide fuel cells (ITSOFCs); Electrolyte; Electrochemical impedance spectroscopy (EIS); Barium zirconate (BaZrO3); Barium cerate (BaCeO3); Solid-state reaction (SSR); Sintering; Conventional sintering (CS); Solid-state reactive sintering (SSRS); Spark plasma sintering (SPS); Ionic conductivity; Oxygen ion conductivity; Proton conductivity; Electronic conductivity; Oxygen ion conductor; Proton conductor; Oxygen partial pressure (OPP); Composite electrolyte
National Category
Ceramics
Research subject
Materials Science and Engineering
Identifiers
URN: urn:nbn:se:kth:diva-165073ISBN: 978-91-7595-517-9 (print)OAI: oai:DiVA.org:kth-165073DiVA: diva2:807057
Public defence
2015-05-20, B2, Brinellvägen 23, KTH, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

QC 20150423

Available from: 2015-04-23 Created: 2015-04-22 Last updated: 2015-06-01Bibliographically approved
List of papers
1. Preparation of Potential Protonic Conductor Yttria Doped Hafnia by Using the Modified Solid State Reaction Method
Open this publication in new window or tab >>Preparation of Potential Protonic Conductor Yttria Doped Hafnia by Using the Modified Solid State Reaction Method
2014 (English)In: ECS Transactions, 2014, Vol. 59 (1), 315-320 p.Conference paper, Published paper (Refereed)
Abstract [en]

A pure and well crystalized yttrium doped hafnium oxide Hf0.69Y0.31O2-δ (YSH) is obtained by using a modified solid state reaction method, where a water-based milling medium and freeze drying are implemented to reduce the agglomeration. The mean sizes of the YSH powder, which is obtained through a traditional alcohol-based milling method, is more than 1 um. However, the powder size can be reduced to 100 nm by using the water-based milling method. In addition, the calcination temperature can be lowered 200 °C to get a pure phase by using the water-based milling method, compared to the alcohol-based milling method. The relative density of YSH ceramic materials can reach to 97.5% by conventional sintering at 1650 °C after during 10 h.

National Category
Ceramics
Research subject
Materials Science and Engineering
Identifiers
urn:nbn:se:kth:diva-165066 (URN)10.1149/05901.0315ecst (DOI)2-s2.0-84920598101 (Scopus ID)
Conference
2014 Electrochemical Conference on Energy & the Environment (ECEE2014)
Note

QC 20150422

Available from: 2015-04-22 Created: 2015-04-22 Last updated: 2015-04-23Bibliographically approved
2. Preparation of 30 mol.% Y-doped hafnia (Hf0.7Y0.3O2-delta) using a modified solid-state reaction method
Open this publication in new window or tab >>Preparation of 30 mol.% Y-doped hafnia (Hf0.7Y0.3O2-delta) using a modified solid-state reaction method
2015 (English)In: Ceramics International, ISSN 0272-8842, E-ISSN 1873-3956, Vol. 41, no 2, 2611-2615 p.Article in journal (Refereed) Published
Abstract [en]

A pure and well-crystallized Hf0.7Y0.3O2-delta (YSH) powder was synthesized using a modified solid-state reaction method. Water-based milling and freeze drying process were implemented to facilitate powder synthesis and final densification process. The improved powder performance, in aspects of phase development and sintering behaviour, was investigated by systematic comparison between different powder processing procedures. Dense YSH ceramic material with a relative density of 0.975 was successfully obtained using conventional sintering at 1650 degrees C for 10 h. XRD, SEM and EDS were employed to characterize the synthesized powder and dense YSH ceramics. Dense YSH ceramic possesses a fluorite cubic structure with an a value of 5.1406 angstrom, and the ionic radius of Y3+ in YSH was determined to be 0.1006 nm.

Keyword
Solid state reaction, Milling, Sintering, Fuel cells
National Category
Ceramics
Identifiers
urn:nbn:se:kth:diva-161095 (URN)10.1016/j.ceramint.2014.10.036 (DOI)000348961400089 ()2-s2.0-84919443860 (Scopus ID)
Note

QC 20150324

Available from: 2015-03-24 Created: 2015-03-09 Last updated: 2017-12-04Bibliographically approved
3. Preparation of Protonic Conductor BaZr0.5Ce0.3Ln0.2O3-δ (Ln = Y, Sm, Gd, Dy) by using a Solid State Reactive Sintering Method
Open this publication in new window or tab >>Preparation of Protonic Conductor BaZr0.5Ce0.3Ln0.2O3-δ (Ln = Y, Sm, Gd, Dy) by using a Solid State Reactive Sintering Method
2014 (English)Conference paper, Published paper (Refereed)
Abstract [en]

A pure and well crystalized yttrium doped hafnium oxide Hf0.69Y0.31O2-δ (YSH) is obtained by using a modified solid state reaction method, where a water-based milling medium and freeze drying are implemented to reduce the agglomeration. The mean sizes of the YSH powder, which is obtained through a traditional alcohol-based milling method, is more than 1 um. However, the powder size can be reduced to 100 nm by using the water-based milling method. In addition, the calcination temperature can be lowered 200 ℃ to get a pure phase by using the water-based milling method, compared to the alcohol-based milling method. The relative density of YSH ceramic materials can reach to 97.5% by conventional sintering at 1650 ℃ after during 10 h.

Series
Advances in Science and Technology
National Category
Ceramics
Identifiers
urn:nbn:se:kth:diva-165067 (URN)10.4028/www.scientific.net/AST.87.1 (DOI)
Conference
13th International Ceramics Congress (CIMTEC2014)
Note

QC 20150423

Available from: 2015-04-22 Created: 2015-04-22 Last updated: 2015-06-15Bibliographically approved
4. Sintering behaviour of the protonic conductors BaZr(x)Ce(0.8-x)Ln(0.2)O(3-delta) (x=0.8, 0.5, 0.1; Ln=Y, Sm, Gd, Dy) during the solid-state reactive-sintering process
Open this publication in new window or tab >>Sintering behaviour of the protonic conductors BaZr(x)Ce(0.8-x)Ln(0.2)O(3-delta) (x=0.8, 0.5, 0.1; Ln=Y, Sm, Gd, Dy) during the solid-state reactive-sintering process
2015 (English)In: Ceramics International, ISSN 0272-8842, E-ISSN 1873-3956, Vol. 41, no 2, 2558-2564 p.Article in journal (Refereed) Published
Abstract [en]

The protonic conductors BaZr(x)Ce(0.8-x)Ln(0.2)O(3-delta) (x=0.8, 0.5, 0.1; Ln=Y, Sm, Gd, Dy) were successfully prepared using a solid-state reactive-sintering method. NiO (1 wt.%) was added as a sintering aid, and it was proven that NiO produced tremendous enhancement in the densification process. The morphologies of the variously doped BaZr(0.8)Ln(0.2)O(3-delta), BaZr(0.5)Ce(0.3)Ln(0.2)O(3-delta) and BaZr(0.1)Ce(0.7)Ln(0.2)O(3-delta) ceramics, as well as their sintering behaviour, were investigated. The results show that the Ce content in the BaZr(0.8)Ln(0.2)O(3-delta), BaZr(0.5)Ce(0.3)Ln(0.2)O(3-delta) and BaZr(0.1)Ce(0.7)Ln(0.2)O(3-delta) compounds influences the sintering temperature significantly, and a larger Ce content will lead to a lower sintering temperature. In addition, ionic radii of the dopants that are similar to the ionic radii of the B-site will also result in a lowered sintering temperature. Based on the present study, NiO has no influence on the lattice parameters.

Keyword
Solid state reaction, Milling, Sintering, Fuel cells
National Category
Materials Engineering
Identifiers
urn:nbn:se:kth:diva-161094 (URN)10.1016/j.ceramint.2014.10.177 (DOI)000348961400080 ()2-s2.0-84919443842 (Scopus ID)
Note

QC 20150324

Available from: 2015-03-24 Created: 2015-03-09 Last updated: 2017-12-04Bibliographically approved
5. Ionic conductivity of dense BaZr(0.5)Ce(0.3)Ln(0.2)O(3-delta) (Ln = Y, Sm, Gd, Dy) electrolytes
Open this publication in new window or tab >>Ionic conductivity of dense BaZr(0.5)Ce(0.3)Ln(0.2)O(3-delta) (Ln = Y, Sm, Gd, Dy) electrolytes
2014 (English)In: Journal of Power Sources, ISSN 0378-7753, E-ISSN 1873-2755, Vol. 272, 786-793 p.Article in journal (Refereed) Published
Abstract [en]

BaZr(0.5)Ce(0.3)Ln(0.2)O(3-delta) (BZCLn532, Ln = Y, Sm, Gd, Dy) based electrolytes were successfully synthesized by a cost-effective solid-state reactive sintering (SSRS) method while using 1.0 wt.% NiO as a sintering aid. Dense pellets of BZCLn532 compounds can be prepared at sintering temperatures of 1600 degrees C (BZCY532) and 1400 degrees C (BZCS532, BZCG532 and BZCD532). The conductivities of the dense BZCLn532 ceramics were tested in dry and wet air at temperatures of 700 degrees C-200 degrees C. On the basis of the obtained results, it could be concluded that the BZCY532-based electrolyte show promise for use as oxygen-ion conductors and proton conductors in intermediate temperature solid oxide fuel cells (ITSOFCs).

Keyword
Barium cerate, Barium zirconate, Solid-state reactive sintering, Proton conductivity
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-157587 (URN)10.1016/j.jpowsour.2014.09.056 (DOI)000344208700097 ()2-s2.0-84907279875 (Scopus ID)
Note

QC 20141215

Available from: 2014-12-15 Created: 2014-12-11 Last updated: 2017-12-05Bibliographically approved
6. The effect of NiO on the conductivities of BaZr0.5Ce0.3Y0.2O3-δ based electrolytes
Open this publication in new window or tab >>The effect of NiO on the conductivities of BaZr0.5Ce0.3Y0.2O3-δ based electrolytes
(English)Manuscript (preprint) (Other academic)
National Category
Ceramics
Identifiers
urn:nbn:se:kth:diva-165068 (URN)
Note

QS 2015

Available from: 2015-04-22 Created: 2015-04-22 Last updated: 2015-04-23Bibliographically approved
7. Novel BaZr0.5Ce0.3Y0.2O3-δ based proton conductors prepared by spark plasma sintering
Open this publication in new window or tab >>Novel BaZr0.5Ce0.3Y0.2O3-δ based proton conductors prepared by spark plasma sintering
(English)Manuscript (preprint) (Other academic)
National Category
Ceramics
Identifiers
urn:nbn:se:kth:diva-165069 (URN)
Note

QS 2015

Available from: 2015-04-22 Created: 2015-04-22 Last updated: 2015-04-23Bibliographically approved

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