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Strontium diffusion in magnetron sputtered gadolinia-doped ceria thin film barrier coatings for solid oxide fuel cells
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
Danish Technological Institute, Aarhus, Denmark.
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2013 (English)In: Advanced Energy Materials, E-ISSN 1614-6840, Vol. 3, no 7, 923-929 p.Article in journal (Refereed) Published
Abstract [en]

Strontium (Sr) diffusion in magnetron sputtered gadolinia-doped ceria (CGO) thin films is investigated. For this purpose, a model system consisting of a screen printed (La,Sr)(Co,Fe)O3−δ (LSCF) layer, and thin films of CGO and yttria-stabilized zirconia (YSZ) is prepared to simulate a solid oxide fuel cell. This setup allows observation of Sr diffusion by observing SrZrO3 formation using X-ray diffraction while annealing. Subsequent electron microscopy confirms the results. This approach presents a simple method for assessing the quality of CGO barriers without the need for a complete fuel cell test setup. CGO films with thicknesses ranging from 250 nm to 1.2 μm are tested at temperatures from 850 °C to 950 °C which yields an in-depth understanding of Sr diffusion through CGO thin films that may be of high scientific and technical interest for implementation of novel fuel cell materials. Sr is found to diffuse along column/grain boundaries in the CGO films but by modifying the film thickness and microstructure the breaking temperature of the barrier can be increased.

Place, publisher, year, edition, pages
John Wiley & Sons, 2013. Vol. 3, no 7, 923-929 p.
Keyword [en]
Ce0.9Gd0.1O2−δ; CGO; GDC; Sr diffusion; X-ray diffraction
National Category
Natural Sciences
Identifiers
URN: urn:nbn:se:liu:diva-84610DOI: 10.1002/aenm.201300003ISI: 000327698200015OAI: oai:DiVA.org:liu-84610DiVA: diva2:560641
Note

On the day of the defence date the status of this article was Manuscript.

Available from: 2012-10-15 Created: 2012-10-15 Last updated: 2017-04-10Bibliographically approved
In thesis
1. Physical Vapor Deposition of Yttria-Stabilized Zirconia and Gadolinia-Doped Ceria Thin Films for Fuel Cell Applications
Open this publication in new window or tab >>Physical Vapor Deposition of Yttria-Stabilized Zirconia and Gadolinia-Doped Ceria Thin Films for Fuel Cell Applications
2012 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

In this thesis, reactive sputter deposition of yttria-stabilized zirconia (YSZ) and cerium gadolinium oxide (CGO) thin films for solid oxide fuel cell (SOFC) applications have been studied. All films have been deposited under industrial conditions.

YSZ films were deposited on silicon wafers as well as commercial NiO-YSZ fuel cell anodes. The texture, morphology, and composition of the deposited films were investigated with respect to deposition parameters such as bias voltage which was identified as a key parameter to tailor the texture of the film and promote less columnar coatings when depositing on Si. In contrast, films grown on NiO-YSZ fuel cell anodes were seen to be randomly orientated when deposited at low substrate bias voltages. When the bias voltage was increased the film took over the orientation of underlying substrate due to substrate template effects. The deposited coatings were found to be homogeneous large areas within the coating zone, which is highly important for industrial applications.

The performance of sputtered CGO thin films as diffusion barriers for stopping Sr diffusion between SOFC cathodes and electrolytes was also studied. This was done by introducing the sputtered CGO films in a metal-based SOFC setup. The performance depended on the density of the barrier layer, signifying that Sr diffusion and SrZrO3 formation is an issue. Area specific resistances down to 0.27 Ωcm2, corresponding to a maximum power density up to 1.14 W cm−2 at 650 °C could be obtained with sputtered CGO barrier layers in combination with Sr-doped lanthanum cobalt oxide cathodes which is a significant improvement compared conventional ceramic SOFCs.

The diffusion mechanism of Sr through sputtered CGO films was investigated. For this purpose, a model system simulating a SOFC was prepared by depositing CGO and YSZ on cathode material. This setup allowed observation of Sr diffusion by observing SrZrO3 formation using X-ray diffraction while annealing. Electron microscopy was subsequently performed to confirm the results. It was found that Sr diffused along column/grain boundaries in the CGO films but by modifying the film thickness and microstructure the breaking temperature of the barrier could be increased.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2012. 40 p.
Series
Linköping Studies in Science and Technology. Thesis, ISSN 0280-7971 ; 1552
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-84611 (URN)LIU-TEK-LIC-2012:37 (Local ID)978-91-7519-767-8 (ISBN)LIU-TEK-LIC-2012:37 (Archive number)LIU-TEK-LIC-2012:37 (OAI)
Presentation
2012-11-12, Planck, Fysikhusete, Campus Valla, Linköpings universitet, Linköping, 10:15 (Swedish)
Opponent
Supervisors
Available from: 2012-10-15 Created: 2012-10-15 Last updated: 2015-01-13Bibliographically approved
2. Yttria-Stabilized Zirconia and Gadolinia-Doped Ceria Thin Films for Fuel Cell Applications
Open this publication in new window or tab >>Yttria-Stabilized Zirconia and Gadolinia-Doped Ceria Thin Films for Fuel Cell Applications
2014 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Solid oxide fuel cells convert chemical energy directly into electrical energy with high efficiency and low emission of pollutants. However, before fuel cell technology can gain a significant share of the electrical power market, the operation temperature needs to be reduced in order to decrease costs and improve the durability of the cells. Application of thin film electrolytes and barrier coatings is a way of achieving this goal.

In this thesis, I have investigated film growth and microstructure of yttria-stabilized zirconia (YSZ) and gadolinia-doped ceria (CGO) thin films deposited by physical vapor deposition. The aim is to make industrially applicable coatings suitable for application in solid oxide fuel cells (SOFCs). For this purpose, the coatings need to be thin and dense. YSZ coatings were prepared by pulsed direct current (DC) magnetron sputtering and high power impulse magnetron sputtering (HiPIMS) in both laboratory- and industrial-scale setups.

Industrial-scale pulsed DC magnetron sputtering of YSZ showed that homogenous coating over large areas was possible. In order to increase film density of the YSZ, HiPIMS was used. By tuning deposition pressure, peak power density and substrate bias voltage it was possible to deposit noncolumnar thin films without voids and cracks as desired for SOFC applications.

CGO coatings were deposited by pulsed DC magnetron sputtering with the purpose of implementing diffusion barriers to prevent reactions between Sr from the SOFC cathode and the electrolyte. A model system simulating a SOFC was prepared by depositing thin CGO and YSZ layers on cathode material. This setup allowed the study of Sr diffusion by observing SrZrO3 formation using X-ray diffraction while annealing. Electron microscopy was subsequently performed to confirm the results. The study revealed Sr to diffuse along column/grain boundaries in the CGO films but by modifying the film thickness and microstructure the breaking temperature of the barrier could be increased.

CGO thin films were implemented in metal-based SOFC and the influence of film microstructure and thickness on the electrochemical performance of the cell was studied. Cell tests showed that an area specific resistance (ASR) down to 0.27 Ωcm2 could be obtained 650 °C with sputtered CGO barrier layers in combination with a lanthanum strontium cobaltite cathode. In comparison a spin-coated CGO barrier resulted in an ASR value of 0.50 Ωcm2. This shows the high effectiveness of the sputtered barrier in obtaining state-of-the-art performance.

In summary, this work provides fundamental understanding of the deposition and growth of YSZ and CGO thins films and proves the prospective of employing thin film barrier coating in order to obtain high-performing SOFCs.  

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2014. 63 p.
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1564
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-102513 (URN)10.3384/diss.diva-102513 (DOI)978-91-7519-441-7 (ISBN)
Public defence
2014-02-25, Planck, Fysikhuset, Campus Valla, Linköpings universitet, Linköping, 10:15 (English)
Opponent
Supervisors
Available from: 2013-12-12 Created: 2013-12-12 Last updated: 2015-01-13Bibliographically approved

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Sønderby, SteffenLunca Popa, PetruLu, JunEklund, Per

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