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TECHNICAL PAPERS

Plasma Sprayed Diffusion Barrier Layers Based on Doped Perovskite-Type LaCrO3 at Substrate-Anode Interface in Solid Oxide Fuel Cells

[+] Author and Article Information
T. Franco1

 German Aerospace Center (DLR), Institute of Technical Thermodynamics, Pfaffenwaldring 38-40, 70569 Stuttgart, Germanythomas.franco@dlr.de

Z. HoshiarDin, P. Szabo, M. Lang, G. Schiller

 German Aerospace Center (DLR), Institute of Technical Thermodynamics, Pfaffenwaldring 38-40, 70569 Stuttgart, Germany

1

Corresponding author.

J. Fuel Cell Sci. Technol 4(4), 406-412 (May 02, 2006) (7 pages) doi:10.1115/1.2756846 History: Received December 08, 2005; Revised May 02, 2006

In the thin-film solid oxide fuel cell (SOFC) concept of the German Aerospace Center (DLR) in Stuttgart, the entire membrane electrode assembly (MEA) is deposited onto a porous metallic substrate by an integrated multistep vacuum plasma spray (VPS) process. This concept enables the production of very thin and stable electrodes and electrolyte layers with a total cell thickness of only 100120μm. In this concept, the porous ferrite substrate material predominantly acts as mechanical cell support and as fuel gas distributor. In general, ferrite substrate alloys with high chromium and low manganese content show both excellent corrosion stability and adequate thermal expansion behavior. Nevertheless, at the high process temperature in the SOFC of 800°C, atomic transport processes can show a detrimental effect on cell performance, at least at the required long-term operation. Problems arise, in particular, through diffusion processes of Fe-, Cr-, and Ni-species between the Ni/8YSZ anode and the ferrite steel-based substrate material. This can induce significant structure changes both in the anode and the substrate. As a reliable solution of this key problem, a plasma sprayed thin diffusion barrier layer is seen at the interface between anode and substrate, which consists of an electrically conductive and chemically stable ceramic component. For this purpose, some doped perovskite-type LaCrO3, such as La1xSrxCrO3δ, La1xCaxCrO3δ, or La1xSrxCr1yCoyO3δ were investigated and tested carefully at DLR. These types of perovskites show a high potential to fulfill all the required properties that are needed for the applicability as an anode-side diffusion barrier layer. The paper focuses on basic investigations of differently doped LaCrO3 compounds under SOFC-relevant conditions concerning thermal expansion, electrical conductivity, chemical stability, etc. Furthermore, first results of electrically and electrochemically characterized half cells carried out with some qualified doped LaCrO3 are shown. Finally, the diffusion barrier layer is demonstrated as a new SOFC component that is effective at cell operating conditions.

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Copyright © 2007 by American Society of Mechanical Engineers
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Figures

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Figure 1

Layer formation on a substrate (left) (5) and principle of a DC-plasma torch with Laval nozzle M3 (right)

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Figure 2

Principle of the planar metal substrate supported SOFC concept of DLR-Stuttgart

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Figure 3

EDX-map of an interface (cross section) “substrate/anode” of a substrate supported cell after 250h of operating time. Element distribution: iron, Fe (blue), chromium, Cr (green), nickel, Ni (red).

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Figure 4

Diffusion tracks on the anode side in SOFCs at cell operation

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Figure 5

Diffusion inhibiting or barrier layer as a new cell component integrated in the substrate supported DLR SOFC concept

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Figure 6

SEM of a typical La0.7Sr0.3CrO3-powder (particle size distribution (PSD): −60+20μm) for plasma spray experiments (left) and OM cross section of a plasma sprayed diffusion barrier layer on Al2O3-substrate for conductivity measurements (right)

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Figure 7

Temperature dependence of the specific electrical conductivity of differently doped LaCrO3-perovskites measured in Ar‐5%H2-atmosphere (left) and Arrhenius-type plot with calculated activation energies Ea (right)

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Figure 9

EDX-map of a substrate-anode interface with La0.7Sr0.15Ca0.15CrO3-barrier layer of a substrate-supported half cell after 400h of area-specific contact resistance measurements at 800°C and 200mA∕cm2 in Ar‐5%H2‐2%H2O. Element distribution: nickel, Ni (red), chromium, Cr (green), iron, Fe (blue).

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Figure 10

Cross section of a plasma sprayed cell with adapted structure of the LaCrO3-diffusion barrier layer

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Figure 8

Time dependence of the specific electrical conductivity of differently doped LaCrO3-perovskites measured in Ar‐5%H2-atmosphere at 800°C

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