In Situ Observations of Microstructural Changes in SOFC Anodes during Redox Cycling

Klemensø, Trine; Appel, C.C.; Mogensen, Mogens Bjerg

doi:10.1149/1.2214303

Cited by 79 publications

(55 citation statements)

References 19 publications

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“…From in-situ ESEM (environmental scanning electron microscopy) studies it has been observed that re-oxidation of the Ni grains involves reorganization of the Ni/NiO phase [22]. If the Nioxidation proceeded fast (i.e.…”

Section: Discussionmentioning

confidence: 99%

Ni–YSZ Solid Oxide Fuel Cell Anode Behavior Upon Redox Cycling Based on Electrical Characterization

Klemensø

Mogensen

2007

Journal of the American Ceramic Society

103

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Nickel (Ni)—yttria‐stabilized zirconia (YSZ) cermets are a prevalent material used for solid oxide fuel cells. The cermet degrades upon redox cycling. The degradation is related to microstructural changes, but knowledge of the mechanisms has been limited. Direct current conductivity measurements were performed on cermets and cermets where the Ni component was removed. Measurements were carried out before, during, and after redox cycling the cermet. The cermet conductivity degraded over time due to sintering of the nickel phase. Following oxidizing events, the conductivity of the cermets improved, whereas the conductivity of the YSZ phase decreased. An improved model of the redox degradation mechanism was established based on the measurements.

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Section: Discussionmentioning

confidence: 99%

Ni–YSZ Solid Oxide Fuel Cell Anode Behavior Upon Redox Cycling Based on Electrical Characterization

Klemensø

Mogensen

2007

Journal of the American Ceramic Society

103

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“…A model for the redox mechanism in Ni-YSZ anodes has been developed and reported by Klemensø et al [10,11]. In this model the change in Ni-YSZ-cermet microstructure is explained by reorganisation and agglomeration of the Ni particles upon reduction.…”

Section: Mechanismmentioning

confidence: 99%

Characterisation of Ni–YSZ‐Cermets with Respect to Redox Stability

2007

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In anode‐supported solid oxide fuel cells (SOFCs), air break‐in on the anode side can result in reoxidation of metallic nickel. The volume expansion caused by Ni oxidation generates stresses within the substrate, the anode and the electrolyte. Those stresses exceed the stability of the components, potentially promoting crack growth. Therefore, either the SOFC degrades continuously after each redox‐cycle or the membrane electrode assembly (MEA) fails completely if the electrolyte cracks. The influence of several reoxidation parameters on the mechanical integrity of Ni–YSZ‐anodes after reoxidation was investigated using different types of samples. All samples were SFEs (substrate–functional layer–electrolytes), consisting of Ni–YSZ‐substrate, Ni–YSZ‐anode and YSZ‐electrolyte. Investigations were carried out on freestanding SFEs and SFEs attached to steel plates (Crofer22APU, Thyssen Krupp V. D. M., Material Data Sheet No. 4046, Edition of December 2006) with a glass sealing. The results show a big influence of the degree of oxidation, homogeneity of oxidation, the operating temperature and the incident flow on the behaviour and the mechanical integrity of the reoxidised SFEs. The time of oxidation and the gas flow rate were influencing parameters, whereas the influence of the porosity was insignificant. The behaviour of the SFEs upon reoxidation also changes dramatically when comparing freestanding samples with attached samples.

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“…In situ microstructural changes have been observed using an environmental scanning electron microscope (ESEM) (13). This study showed a shrinkage of the Ni phase during NiO reduction.…”

Section: Introductionmentioning

confidence: 99%

In situ Reduction and Oxidation of Nickel from Solid Oxide Fuel Cells in a Transmission Electron Microscope

Faes¹,

Jeangros²,

Wagner³

et al. 2009

ECS Trans.

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Environmental transmission electron microscopy was used to characterize in situ the reduction and oxidation of nickel from a Ni/YSZ solid oxide fuel cell anode support between 300-500°C. The reduction is done under low hydrogen pressure. The reduction initiates at the NiO/YSZ interface, then moves to the center of the NiO grain. At higher temperature the reduction occurs also at the free NiO surface and the NiO/NiO grain boundaries. The growth of Ni is epitaxial on its oxide. Due to high volume decrease, nanopores are formed during reduction. During oxidation, oxide nanocrystallites are formed on the nickel surface. The crystallites fill up the nickel porosity and create an inhomogeneous structure with remaining voids. This change in structure causes the nickel oxide to expand during a RedOx cycle.

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In Situ Observations of Microstructural Changes in SOFC Anodes during Redox Cycling

Cited by 79 publications

References 19 publications

Ni–YSZ Solid Oxide Fuel Cell Anode Behavior Upon Redox Cycling Based on Electrical Characterization

Ni–YSZ Solid Oxide Fuel Cell Anode Behavior Upon Redox Cycling Based on Electrical Characterization

Characterisation of Ni–YSZ‐Cermets with Respect to Redox Stability

In situ Reduction and Oxidation of Nickel from Solid Oxide Fuel Cells in a Transmission Electron Microscope

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