Aging of atmospherically plasma sprayed chromium evaporation barriers

Vaßen, Robert; Grünwald, Nikolas; Marcano, Diana; Menzler, Norbert H.; Mücke, Robert; Sebold, Doris; Sohn, Yoo Jung; Guillon, Olivier

doi:10.1016/j.surfcoat.2016.02.005

Cited by 25 publications

(24 citation statements)

References 19 publications

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“…[13][14][15][16] However, even with the most effective protective coatings Cr cannot be completely prevented from entering the gas phase and finally reacting with the cathode material. Uncoated balance-of-plant components are an almost unavoidable source of volatile Cr species under SOFC operating conditions.…”

Section: -4mentioning

confidence: 99%

“…11,12 In particular, dense layers applied by atmospheric plasma spraying (APS) have proven able to reduce the Cr deposition on the cathode and thereby considerably lessen degradation. [13][14][15][16] However, even with the most effective protective coatings Cr cannot be completely prevented from entering the gas phase and finally reacting with the cathode material. Uncoated balance-of-plant components are an almost unavoidable source of volatile Cr species under SOFC operating conditions.…”

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confidence: 99%

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Insight into the Reaction Mechanism of (La_0.58Sr_0.40)(Co_0.20Fe_0.80)O_3-δCathode with Volatile Chromium Species at High Current Density in a Solid Oxide Fuel Cell Stack

Beez

Yin

Menzler

et al. 2017

J. Electrochem. Soc.

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Anode-supported solid oxide fuel cells with different Cr protection layers on the metallic interconnect were operated in a short stack at 700 • C for 1240 h. The current density was raised sequentially from 0.5 A cm −2 during the first 240 h of operation to 0.75 A cm −2 for a further 1000 h. After operation, the (La,Sr)(Co,Fe)O 3-δ (LSCF) cathode layers were analyzed with respect to Cr interaction by both wet chemical and microstructural methods. For cells equipped with interconnects coated with a dense APS protection layer, the amount of Cr on the cathode was in the range of a few μg. For cells with a porous WPS coating on the interconnect, the amount of Cr was in the range of 110-160 μg cm −2 and Cr-containing phases were detected by SEM analysis both on top of the cathode layer and also at the LSCF/GDC interface, which has rarely been observed before. In addition, a deterioration of the cathode microstructure near the LSCF/GDC interface was observed. With respect to the high current density during operation, a theory was developed which explains both the Cr deposition at the LSCF/GDC interface and also the deterioration of the cathode. Climate change, limitation of resources, technical and political obstacles associated with nuclear power and changes in the global energy economy are only a few reasons why the world needs alternative concepts for its future energy supply. One key technology offering decentralized energy supply is solid oxide fuel cells (SOFC).1 Their high efficiency; fuel flexibility and scalability allows them to be used as decentralized power plants or, on a smaller scale, in auxiliary power units or range extenders in mobile applications. 2-4During the development and optimization of SOFC stacks and systems, attention was not only focused on performance but also on the application of cost-efficient materials. One major improvement was the establishment of metallic interconnects, offering high electronic and thermal conductivity and mechanical stability while also decreasing the price per repeating unit compared to full ceramic stack designs.5 However, the preferentially used Cr-containing steels lead to pronounced performance degradation due to the evaporation of Cr compounds, which then react with the cathode. Under the oxidizing conditions on the cathode side, hexavalent Cr species such as CrO 3 and CrO 2 (OH) 2 evaporate from the oxide scale of the interconnect or balance-of-plant components and react with the LSCF cathode material to form a Sr-and Cr-containing oxide scale thereby decreasing cell performance. 3,6,7 This effect is known to be influenced by parameters such as Cr partial pressure, air humidity and temperature. [8][9][10] To avoid this Cr-related degradation, different strategies have been developed to either reduce the Cr partial pressure to an acceptable level for the desired operating time or to increase the Cr tolerance of the cathode material itself. The most promising technique for avoiding Cr poisoning is to coat the interconnect steel with a preferentially dense pro...

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Section: -4mentioning

confidence: 99%

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confidence: 99%

Insight into the Reaction Mechanism of (La_0.58Sr_0.40)(Co_0.20Fe_0.80)O_3-δCathode with Volatile Chromium Species at High Current Density in a Solid Oxide Fuel Cell Stack

Beez

Yin

Menzler

et al. 2017

J. Electrochem. Soc.

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“…However, during SOFC operation the formation of volatile Cr oxides and especially oxyhydroxides may deteriorate the cathode and/or the cathode/electrolyte interface . Therefore, various coating types are being used to minimize the formation of volatile Cr species , ; in JÜLICH's standard F10 design an atmospheric plasma sprayed (APS) coating of MCF is being applied .…”

Section: Introductionmentioning

confidence: 99%

Post‐test Characterization of Metallic Materials and Adjacent Components in an SOFC Stack After 34,000 h Operation at 700 °C

et al. 2018

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The present paper describes the electrochemical results and the post exposure microstructural characterization by means of SEM/EDS of a four layer SOFC stack after 34,000 h operation under load at 700 °C, showing low voltage degradation rate less than 0.3% per 1,000 h. Emphasis was put on the behavior of the ferritic interconnect steel and its interaction with glass sealants as well as contacting and coating materials. The interconnect steel had formed thin protective chromia scales. Gas distributing steel foils of 200 µm showed in some locations breakaway type oxidation. It was related to local overheating caused by locally occurring combustion of a defective cell. The interaction of the steel with the glass sealant showed good adhesion. Interdiffusion at the joint between nickel contact and steel interconnect at the anode side resulted in minor oxide formation on the Ni wires and in austenite formation in the steel without formation of σ‐FeCr formation at the steel/austenite interface. The steel showed excellent compatibility with the Manganese‐Cobalt‐Ferrite (MCF) chromium retention coatings. Chromium enriched phases were found near the interface between MCF coating and perovskite contact layer. Excess glass sealing material interacted with the contact layer without showing obvious detrimental effects.

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“…In case of the stack showing a higher degradation rate, a manganese oxide (MnOx) layer was applied by WPS, while the interconnectors of the other stack are coated with an MCF protective coating applied by APS. In contrast to WPS-MnOx layers, it is known that APS-MCF layers are rather dense [19]. From these two stacks it can be concluded that APS-MCF coatings are promising candidates for chromium protection layers (assuming that most of the additional degradation originates from the chromium-cathode interaction).…”

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confidence: 97%

“…Magnetron sputtering enables the deposition of very thin and dense protective layers [11] showing high conductivities but have to prove their stability in the long term and in stack tests. Further research on aerosol deposition [14], electrophoretic deposition [15,16], wet chemical methods [17] or several thermal spray techniques [12,[18][19][20] revealed low chromium diffusion rates. Nevertheless, all protective coatings must exhibit minimum degradation for long-term operation within real stack tests.…”

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Self-healing atmospheric plasma sprayed Mn1.0Co1.9Fe0.1O4 protective interconnector coatings for solid oxide fuel cells

Grünwald

Sebold

Sohn

et al. 2017

Journal of Power Sources

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Dense coatings on metallic interconnectors are necessary to suppress chromium poisoning of SOFC cathodes. Atmospherically plasma sprayed (APS) Mn1.0Co1.9Fe0.1O4 (MCF) protective layers demonstrated reduced chromium related degradation in laboratory and stack tests. Previous analyses revealed strong microstructural changes comparing the coating's as-sprayed and operated condition. This work concentrates on the layerdensification and crack-healing observed by annealing APS-MCF in air, which simulates the cathode operation conditions. The effect is described by a volume expansion induced by a phase transformation. Reducing conditions during the spray process lead to a deposition of the MCF in a metastable rock salt configuration. Annealing in air activates diffusion processes for a phase transformation to the low temperature stable spinel phase (T < 1050 °C). This transformation is connected to an oxygen incorporation which occurs at regions facing high oxygen partial pressures, as there are the sample surface, cracks and pore surfaces. Calculations reveal a volume expansion induced by the oxygen uptake which seals the cracks and densifies the coating. The process decelerates when the cracks are closed, as the gas route is blocked and further oxidation continues over solid state diffusion. The self-healing abilities of metastable APS coatings could be interesting for other applications.

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Aging of atmospherically plasma sprayed chromium evaporation barriers

Cited by 25 publications

References 19 publications

Insight into the Reaction Mechanism of (La_0.58Sr_0.40)(Co_0.20Fe_0.80)O_3-δCathode with Volatile Chromium Species at High Current Density in a Solid Oxide Fuel Cell Stack

Insight into the Reaction Mechanism of (La_0.58Sr_0.40)(Co_0.20Fe_0.80)O_3-δCathode with Volatile Chromium Species at High Current Density in a Solid Oxide Fuel Cell Stack

Post‐test Characterization of Metallic Materials and Adjacent Components in an SOFC Stack After 34,000 h Operation at 700 °C

Self-healing atmospheric plasma sprayed Mn1.0Co1.9Fe0.1O4 protective interconnector coatings for solid oxide fuel cells

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Aging of atmospherically plasma sprayed chromium evaporation barriers

Cited by 25 publications

References 19 publications

Insight into the Reaction Mechanism of (La0.58Sr0.40)(Co0.20Fe0.80)O3-δCathode with Volatile Chromium Species at High Current Density in a Solid Oxide Fuel Cell Stack

Insight into the Reaction Mechanism of (La0.58Sr0.40)(Co0.20Fe0.80)O3-δCathode with Volatile Chromium Species at High Current Density in a Solid Oxide Fuel Cell Stack

Post‐test Characterization of Metallic Materials and Adjacent Components in an SOFC Stack After 34,000 h Operation at 700 °C

Self-healing atmospheric plasma sprayed Mn1.0Co1.9Fe0.1O4 protective interconnector coatings for solid oxide fuel cells

Contact Info

Product

Resources

About

Insight into the Reaction Mechanism of (La_0.58Sr_0.40)(Co_0.20Fe_0.80)O_3-δCathode with Volatile Chromium Species at High Current Density in a Solid Oxide Fuel Cell Stack

Insight into the Reaction Mechanism of (La_0.58Sr_0.40)(Co_0.20Fe_0.80)O_3-δCathode with Volatile Chromium Species at High Current Density in a Solid Oxide Fuel Cell Stack