| 1. |
- Grolig, Jan Gustav, 1986, et al.
(författare)
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Coated stainless steel 441 as interconnect material for solid oxide fuel cells: Evolution of electrical properties
- 2015
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Ingår i: Journal of Power Sources. - : Elsevier BV. - 0378-7753. ; 284, s. 321-327
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Tidskriftsartikel (refereegranskat)abstract
- AISI 441 coated. with a double layer coating of 10 nm cerium (inner layer) and 630 nm cobalt was investigated and in addition the uncoated material was exposed for comparison. The main purpose of this investigation was the development of a suitable ASR characterization method. The material was exposed to a simulated cathode atmosphere of air with 3% water at 850 degrees C and the samples were exposed for up to 1500 h. We compared two methods of ASR measurements, an in-situ method where samples were measured with platinum electrodes for longer exposure times and an ex-situ method where pre-oxidized samples were measured for only very short measurement times. It was found that the ASR of ex-situ characterized samples could be linked to the mass gain and the electrical properties could be linked to the evolving microstructure during the different stages of exposure. Both the degradation of the electric performance and the oxygen uptake (mass gain) followed similar trends. After about 1500 h of exposure an ASR value of about 15 m Omega cm(2) was reached. The in-situ measured samples suffered from severe corrosion attack during measurement. After only 500 h of exposure already a value of 35 m Omega cm(2) was obtained.
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| 2. |
- Grolig, Jan Gustav, 1986, et al.
(författare)
-
Copper Iron Conversion Coating for Solid Oxide Fuel Cell Interconnects
- 2015
-
Ingår i: Journal of Power Sources. - : Elsevier BV. - 0378-7753. ; 297, s. 534-539
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Tidskriftsartikel (refereegranskat)abstract
- A conversion coating of iron and copper was investigated with the purpose of increasing the performance of Sanergy HT as a potential SOFC interconnect material. Samples were exposed to a simulated cathode atmosphere (air, 3 % H2O) for durations of up to 1000 h at 850 °C. Their performance in terms of corrosion, chromium evaporation and electrical resistance (ASR) was monitored and compared to uncoated and cobalt-coated Sanergy HT samples. The copper iron coating had no negative effects on corrosion protection and decreased chromium evaporation by about 80%. An Area Specific Resistance (ASR) of 10 mΩcm2 was reached after 1000 h of exposure. Scanning Electron Microscopy revealed well adherent oxide layers comprised of an inner chromia layer and an outer spinel oxide layer.
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| 3. |
- Grolig, Jan Gustav, 1986, et al.
(författare)
-
Effect of Cerium on the Electrical Properties of a Cobalt Conversion Coating for Solid Oxide Fuel Cell Interconnects - A Study Using Impedance Spectroscopy
- 2015
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Ingår i: Electrochimica Acta. - : Elsevier BV. - 0013-4686. ; 184, s. 301-307
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Tidskriftsartikel (refereegranskat)abstract
- Coatings of metallic cobalt, which convert into a cobalt manganese spinel oxide are known to improve the properties of interconnects for solid oxide fuel cells (SOFCs). The addition of cerium to the cobalt coating further improves the corrosion properties of the material. For this study traditional four-point DC measurements at high temperatures were combined with impedance spectroscopy at low temperatures in order to investigate the effect of cerium on the electrical properties of a cobalt conversion coating. It was found that combination-coatings of cerium and cobalt exhibit superior electrical properties compared to pure cobalt coatings. Cerium slows down the growth of chromia and prevents the outward diffusion of iron into the cobalt spinel layer. Both effects are beneficial for the electrical properties of the interconnect. Impedance spectroscopy measurements revealed that even after more than 3000 h of exposure the outer cobalt manganese spinel layer still has a higher electrical conductivity when cerium was present.
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| 4. |
- Grolig, Jan Gustav, 1986
(författare)
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Coated Ferritic Stainless Steels as Interconnects in Solid Oxide Fuel Cells - Material Development and Electrical Properties
- 2015
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Solid oxide fuel cells (SOFCs) are attracting increasing interest as devices with potentialuses in decentralized and clean electricity and heat production. Several challengeswith respect to materials have to be overcome to achieve efficiencies and life-spansthat are sufficient for long-term applications.An important element of an SOFC stack is the interconnect component, which connectstwo adjacent fuel cell elements. Interconnects, which are commonly composedof ferritic stainless steels, have to be corrosion-resistant, mechanically stable and costoptimized.This work aimed to investigate economic solutions for interconnect materials and tounderstand the underlying mechanisms of degradation and electrical conduction ofthese materials. Mainly two substrates, a commercially available steel (AISI 441) anda ferritic stainless steel that was optimized for an SOFC application (Sandvik SanergyHT) were combined with different barrier coatings and exposed to a cathode-sideatmosphere. A method was developed that allows for the electrical characterizationof promising material systems and model alloys, thereby facilitating a fundamentalunderstanding of the dominant electrical conduction processes linked to the oxidescales that grow on interconnects. The AISI 441 steel coated with reactive elementsand cobalt showed good corrosion and chromium evaporation profiles, while AISI 441coated with cerium and cobalt also had promising electrical properties. The SanergyHT steel was examined with coatings of copper and iron and copper and manganese,respectively. The corrosion and chromium evaporation profiles of Sanergy HT wereimproved by coating with copper and iron. The copper and iron-coated Sanergy HTshowed lower area specific resistance values than cobalt-coated Sanergy HT. Chromia,which is the main constituent of oxide scales, was synthesized using differentmethods. The electrical properties of chromia were found to be sensitive to not onlyimpurities, but also heat treatment. Finally the electrical properties of cobalt- andcobalt cerium-coated Sanergy HT steels were investigated. It was revealed that theaddition of cerium improved the conductivity of the interconnect by both slowingdown chromia growth and preventing the outward diffusion of iron into the spinel.
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