Coated stainless steel 441 as interconnect material for solid oxide fuel cells: Oxidation performance and chromium evaporation

Reactive Element (RE) and RE/cobalt-coated stainless steel AISI 441 was exposed at Solid Oxide Fuel Cell (SOFC) cathode conditions (850 degrees C in air with 3% water content) for up to 500 h. The chromium evaporation was measured by applying the denuder technique. Uncoated material exhibited severe spallation which could be successfully prevented by using cerium or lanthanum coatings. By applying double layer coatings of cerium or lanthanum in combination with cobalt the oxidation rate was decreased and the chromium volatilisation was also about 90% lower than the uncoated material

Reevaluating the Cr Evaporation Characteristics of Ce/Co Coatings for Interconnect Applications

Cathode poisoning by chromium evaporation from the interconnects is one of the major degradation mechanisms in SOFC. Coatings have proved to be very effective in suppressing chromium evaporation on interconnects. The quantification of chromium evaporation is important for determining the chromium consumption in the interconnect and predicting the lifetime of the interconnect. Chromium evaporation of uncoated and Ce/Co coated Crofer 22 APU is reevaluated at 800 C. The chromium evaporation of Ce/Co coatings on steel sheets and precut steels is studied. Coupons cut from Ce/Co coated sheets have uncoated edges, which influence the chromium evaporation measurements. The true chromium evaporation of the coated interconnects is evaluated. The PVD Ce/Co coatings on Crofer 22 APU reduce the chromium evaporation by at least 60 times compared to the uncoated at 800 C

Evaluating candidate materials for balance of plant components in SOFC: Oxidation and Cr evaporation properties

Balance of plant (BOP) components made of metallic materials in solid oxide fuel cells are subject to high-temperature corrosion and are a significant source of volatile chromium species. Prospective Fe and Ni-base alloys, AISI 441, AISI 444, a FeCrAl alloy A197/Kanthal\uae EF101, alloy 600, and alloy 800H are investigated for their suitability to BOP components. Oxidation kinetics and chromium evaporation were employed to study the selected alloys at 650 \ub0C and 850 \ub0C for 500 h. A197 performed the best while AISI 441 and AISI 444, performed the worst. Pre-oxidation significantly improved the performance of the alloys at 650 ⁰C

Coated stainless steel 441 as interconnect material for solid oxide fuel cells: Evolution of electrical properties

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

Effect of Hydrogen on the Internal Oxidation of a Pd–Cr Alloy in Dual-Atmosphere Conditions

The effect of hydrogen on oxygen permeability has been studied in a diluted Pd–Cr alloy in dual- and single- atmosphere conditions between 600 and 950\ua0\ub0C. The 0.3\ua0mm thick Pd–1.5Cr foil was exposed in dry and humid air as well as in dual-atmosphere conditions, with one sample surface being exposed to air and one to hydrogen, as encountered in solid oxide fuel cells. At all temperatures, Cr oxidized internally forming internal oxidation zones which were measured in metallographic cross sections. Below 800\ua0\ub0C, an external layer of PdO formed on the surface decreasing the internal oxidation kinetics. No measurable effect of hydrogen on the internal oxidation of Cr in Pd has been detected

Investigation of coated FeCr steels for application as solid oxide fuel cell interconnects under dual-atmosphere conditions

Dual-atmosphere conditions are detrimental for the ferritic stainless steel interconnects used in solid oxide fuel cells, resulting in non-protective oxide scale growth on the air side. In this paper, low-cost steels AISI 441 and AISI 444 and the tailor-made Crofer 22 APU, were investigated at 800 \ub0C and 600 \ub0C under dual-atmosphere conditions: air-3%H2O on one side and Ar-5%H2-3%H2O on the other side. At 800 \ub0C, the uncoated and Ce/Co-coated steels formed protective layers of (Cr,Mn)3O4/Cr2O3 and (Co,Mn)3O4/Cr2O3 respectively on the air side after 336 h. However, at 600 \ub0C, the Ce/Co-coated AISI 441 and AISI 444 showed ∼20–25 μm thick Fe2O3/(Fe,Cr)3O4 oxide scale on the air side after 336 h. Ce/Co coated Crofer 22 APU remained protective after 772 h at 600 \ub0C, indicating better resistance to the dual-atmosphere. The effect of Ce/Co coatings on the air side and the need for coatings on the fuel side are discussed and compared with experimental data

Internal Oxidation of a Fe-Cr Binary Alloy at 700-900 degrees C: The Role of Hydrogen and Water Vapor

Internal oxidation of Fe-2.25Cr has been studied in Fe/FeO Rhines pack (RP) and H-2/H2O gas mixtures at 700-900 degrees C. A novel exposure technique allowing RP experiments in dual atmosphere conditions was developed. No measurable effect of hydrogen on lattice oxygen permeability in ferrite could be detected: neither in single nor in dual atmosphere conditions. The H-2/H2O atmosphere was found to induce stronger oxidation attack at alloy grain boundaries resulting in a morphology similar to intergranular stress corrosion cracking often reported in nuclear technology. The intergranular oxidation attack was demonstrated to be independent of the dual atmosphere effect, i.e., hydrogen dissolved in the alloy

Evaluation of the oxidation and Cr evaporation properties of selected FeCr alloys used as SOFC interconnects

In recent years, a number of ferritic interconnect materials for use in solid oxide fuel cells (SOFC) have been developed and are now commercially available. Although similar, there are substantial variations in minor alloying elements. This study compares the oxidation performance of five such interconnect materials: Crofer 22 H, Crofer 22 APU (ThyssenKrupp VDM), Sanergy HT (Sandvik Materials Technology), ZMG232 G10 (Hitachi Metals) and E-Brite (ATI Allegheny Ludlum). 1000 h exposures have been carried out in tubular furnaces at 850 degrees C, with 6 l/min airflow and 3% H2O to simulate the air side atmosphere in an SOFC. In addition to the oxidation tests, time resolved in-situ chromium evaporation measurements have been carried out using a novel denuder technique. It was found that higher Mn concentrations in the alloy lead to lower Cr evaporation. Nonetheless, all steels exhibit substantial Cr volatilization and coatings are needed for most SOFC applications. Furthermore, this study demonstrates that the mass gain data alone can be misleading, and the mass loss due to Cr volatilization needs to be taken into account. Neglecting Cr evaporation results in an underestimation of the oxidation rate by between 15% and 200% for the studied steel grades

11–23% Cr steels for solid oxide fuel cell interconnect applications at 800 \ub0C – How the coating determines oxidation kinetics

The present work investigates the low-cost steels AISI 441, AISI 430, and AISI 444 against the tailor-made high Cr steel Crofer 22 APU (22.9 wt% Cr) at 800 \ub0C in simulated solid oxide fuel cell (SOFC) cathode conditions. Furthermore, a low Cr steel, AISI 409 (11.4 wt% Cr) is included in the study. The oxidation, chromium evaporation, and area-specific resistance (ASR) of the uncoated and Ce/Co-coated steels are studied for up to 3000 h. Ce/Co-coated steels showed significant improvement in behaviour compared to their uncoated counterparts. The oxidation and chromium evaporation behaviour between the uncoated steels varied substantially while the Ce/Co coated steels exhibited highly similar behaviour. The area-specific resistance of the coated low-cost steels was on par with Crofer 22 APU. However, 430 formed a continuous silica layer, resulting in a higher ASR after 3000 h. Cross-sections of the uncoated and Ce/Co-coated steels were analysed using a scanning electron microscope and energy dispersive X-ray spectroscopy

Novel coatings for protecting solid oxide fuel cell interconnects against the dual-atmosphere effect

A key component of a Solid Oxide Fuel Cell (SOFC) is the interconnect, which connects individual fuel cells in series to form a fuel cell stack to reach a desired electrical potential. The interconnect is exposed to air and fuel in parallel, these so-called dual-atmosphere conditions give rise to especially severe corrosion on the air-side. This work investigates coatings to mitigate this effect. Physical Vapour Deposition (PVD) CeCo-coated AISI 441 samples on the air-side and PVD metallic Al- and Al2O3-coated AISI 441 samples on the fuel-side were exposed under dual-atmosphere conditions for up to 7000 h. The evolution of the corrosion products was followed every 1000 h with an optical microscope. Scanning electron microscopy and energy-dispersive x-ray spectroscopy were performed on cross-sections of the samples after 3000 h of exposure. The SEM analysis showed that coating on the air-side improved the sample\u27s life-time by reducing the level of Cr evaporation even in a dual-atmosphere. The use of fuel-side coatings suppressed the dual-atmosphere effect since the coatings formed a barrier to hydrogen permeation. The best results were observed with metallic Al and Al2O3 coating on the fuel-side, which drastically reduced the dual-atmosphere effect. However, the poor conductivity of Al2O3 makes its use as a coating challenging