Metallic materials in Solid Oxide Fuel Cells: Oxidation and chromium evaporation properties

Solid oxide fuel cells (SOFCs) are high-temperature energy conversion devices which have great potential due to their high efficiency, low operating costs and flexibility in using conventional hydrocarbon based fuels. However, system cost, durability and performance stability in long-term operation are barriers to the widespread commercialization of SOFC technology.Due to the high-temperature operation and aggressive environment in SOFCs, metallic materials - used for interconnects and balance of plant (BOP) - are subject to corrosion. Interconnects are typically made of ferritic stainless steel, which forms a protective chromia scale at high temperatures. This results in two main degradation mechanisms: 1) chromium evaporation, which leads to cathode poisoning and 2) chromia scale growth, which leads to increased electrical resistance. To date, research into metallic materials in SOFC has focused mostly on interconnects. However, metallic materials used inBOP components can be a significant source of volatile chromium species and are often overlooked. The aim of this thesis is to find high performance, cost-effective metallic materials for SOFC systems. Five metallic materials AISI 441, AISI 444, A197/Kanthal\uae EF101, alloy 800H and alloy 600, were studied for potential use in BOP components. Lowcost steels, AISI 441 and AISI 444, and tailor-made Crofer 22 APU in combination with different coatings were evaluated for the interconnect application. Chromium evaporation and oxide-scale growth of the materials are investigated, and the oxide scale is studied further, using XRD, SEM, EDX and ASR.The alumina former, A197, showed the lowest chromium evaporation and oxidation in all exposure conditions. Alloy 800H showed poor oxidation behaviour at lower temperatures but its performance improved significantly after pre-oxidation. Alloy 800H has higher chromium evaporation than A197 but significantly lower than 441 and 444. This low chromium evaporation is due to the formation of an Fe, Ni-rich oxide cap layer. Alloy 600 showed intermediate performance. 441 and 444 showed the highest oxidation and chromium evaporation of the selected alloys, making them a poor choice for BOP components.The uncoated low-cost steels, 441 and 444, showed higher chromium evaporation and/or oxide scale growth than the tailor-made Crofer 22 APU. The oxide scale structure was similar for all the steels, with (Cr, Mn)3O4 spinel on top and Cr2O3 scale underneath after 500 hours. The Ce/Co coated steels showed lower oxide scale growth and a chromium evaporation at least 60 times lower than the uncoated steels. In addition, all the coated steels showed similar chromium evaporation, oxide scale structure ((Co, Mn)3O4 spinel on top and Cr2O3 scale underneath), oxide scale thickness and area specific resistance after 1,000 hours

Metallic materials for solid oxide fuel cells and electrolysers - Mitigating high temperature corrosion

Solid oxide cells (SOCs) are high-temperature energy conversion devices that have great potential due to their high efficiency, low operating costs, and flexibility. SOCs can produce electricity from a variety of fuels as solid oxide fuel cells (SOFCs), and they can convert electricity to fuels as solid oxide electrolyser cells (SOECs). However, the wide-spread commercialisation of this technology is hindered by high system cost, lack of durability, and poor performance stability during long-term operation. Owing to the high-temperature operation and aggressive environment of SOCs, metallic materials used for interconnects and balance of plant (BOP) components are subject to corrosion. Interconnects are typically made of ferritic stainless steel (FSS), which forms a protective chromia scale at high temperatures. The degradation mechanisms, such as Cr (VI) evaporation and chromia scale growth, lead to electrode poisoning and increased electrical resistance, which degrade cell performance.The primary objective of this thesis is to develop alternative materials and understand the degradative mechanisms so as to effectively reduce the costs and improve the performances of metallic materials in SOC systems. The Cr evaporation, oxide scale growth, the microstructural evolution of the oxide scale, and the area-specific resistances are investigated for the selected materials. The majority of the thesis is focused on Ce/Co coatings. Ce/Co-coated, low-cost, commercial FSS (AISI 441, AISI 430, and AISI 444) are compared to tailor-made Crofer 22 APU in air-side atmospheres. Ce/Co-coated steels are further investigated under dual-atmosphere conditions. The Ce/Co coating is compared to various coatings from research laboratories and universities world-wide. Furthermore, the underlying causes for the improvement in the oxidation resistances of FSS that occur in the presence of the reactive element Ce (in the Ce/Co coating) are investigated, and a new mechanism is proposed. Finally, a model to predict the lifetimes of the coated steels is proposed. Moreover, a new coating system, the Ce/FeNi coating, is proposed as an alternative to the Ce/Co coating. The Ce/FeNi coating is found to be more effective than Ce/Co coating in reducing chromia scale growth.While research on metallic materials for SOC has centred on the interconnects, the metallic materials used in BOP components, which can be a significant source of volatile chromium species, have been largely neglected. Five metallic materials (AISI 441, AISI 444, A197/Kanthal\uae EF101, alloy 800H, and alloy 600) are examined for potential usage in BOP components. The oxidation and Cr evaporation behaviours of these materials are discussed and correlated to the observed microstructures

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

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

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

Xeroderma Pigmentosum: Man Deprived of His Right to Light

Xeroderma pigmentosum (XP) is a hereditary autosomal recessive disorder characterized by photo hypersensitivity of sun exposed tissues and subsequent several-fold increased risk for malignant changes resulting from impaired ability to repair UV-induced DNA damage. Estimated incidences vary from 1 in 20,000 in Japan to 1 in 250,000 in the USA, and approximately 2.3 per million live births in Western Europe. Diagnosis is made clinically by the presence of unusual sunburns or lentiginosis or onset of cancers at an early age. It is confirmed by cellular tests for defective DNA repair. Although there is no cure for XP as of now, skin problems can be ameliorated with the use of sunscreens, sun avoidance methods, and recurrent tumor excisions. Oral isotretinoin and topical application of 5-fluorouracil to treat actinic keratoses are other therapeutic options. T4N5 and photolyase liposomal lotions are innovations in the therapy of XP. Genetic counselling implicating the effect of consanguineous marriages should be considered in the management of XP patients

Seabird surveillance: combining CCTV and artificial intelligence for monitoring and research

Ecological research and monitoring need to be able to rapidly convey information that can form the basis of scientifically sound management. Automated sensor systems, especially if combined with artificial intelligence, can contribute to such rapid high-resolution data retrieval. Here, we explore the prospects of automated methods to generate insights for seabirds, which are often monitored for their high conservation value and for being sentinels for marine ecosystem changes. We have developed a system of video surveillance combined with automated image processing, which we apply to common murres Uria aalge. The system uses a deep learning algorithm for object detection (YOLOv5) that has been trained on annotated images of adult birds, chicks and eggs, and outputs time, location, size and confidence level of all detections, frame-by-frame, in the supplied video material. A total of 144 million bird detections were generated from a breeding cliff over three complete breeding seasons (2019-2021). We demonstrate how object detection can be used to accurately monitor breeding phenology and chick growth. Our automated monitoring approach can also identify and quantify rare events that are easily missed in traditional monitoring, such as disturbances from predators. Further, combining automated video analysis with continuous measurements from a temperature logger allows us to study impacts of heat waves on nest attendance in high detail. Our automated system thus produces comparable, and in several cases significantly more detailed, data than those generated from observational field studies. By running in real time on the camera streams, it has the potential to supply researchers and managers with high-resolution up-to-date information on seabird population status. We describe how the system can be modified to fit various types of ecological research and monitoring goals and thereby provide up-to-date support for conservation and ecosystem management

Seabird surveillance: combining CCTV and artificial intelligence for monitoring and research

Ecological research and monitoring need to be able to rapidly convey information that can form the basis of scientifically sound management. Automated sensor systems, especially if combined with artificial intelligence, can contribute to such rapid high-resolution data retrieval. Here, we explore the prospects of automated methods to generate insights for seabirds, which are often monitored for their high conservation value and for being sentinels for marine ecosystem changes. We have developed a system of video surveillance combined with automated image processing, which we apply to common murres Uria aalge. The system uses a deep learning algorithm for object detection (YOLOv5) that has been trained on annotated images of adult birds, chicks and eggs, and outputs time, location, size and confidence level of all detections, frame-by-frame, in the supplied video material. A total of 144 million bird detections were generated from a breeding cliff over three complete breeding seasons (2019–2021). We demonstrate how object detection can be used to accurately monitor breeding phenology and chick growth. Our automated monitoring approach can also identify and quantify rare events that are easily missed in traditional monitoring, such as disturbances from predators. Further, combining automated video analysis with continuous measurements from a temperature logger allows us to study impacts of heat waves on nest attendance in high detail. Our automated system thus produces comparable, and in several cases significantly more detailed, data than those generated from observational field studies. By running in real time on the camera streams, it has the potential to supply researchers and managers with high-resolution up-to-date information on seabird population status. We describe how the system can be modified to fit various types of ecological research and monitoring goals and thereby provide up-to-date support for conservation and ecosystem management

Experimental review of the performances of protective coatings for interconnects in solid oxide fuel cells

Ferritic stainless steel interconnects are used in solid oxide fuel cells; however, coatings are required to improve their performance. Although several types of coatings have been proposed, they have been scarcely investigated under similar conditions. This study compares the characteristics of uncoated Crofer 22 APU and eight different coatings on Crofer 22 APU for up to 3000\ua0h at 800\ua0\ub0C. The coatings were deposited at various research laboratories around the world, and the experiments were performed at Chalmers University of Technology, Sweden. Cross-sections of the samples were analysed using scanning electron microscopy and energy-dispersive x-ray spectroscopy. The (Co,Mn)-based coated steels showed more than 50-fold lower chromium evaporation and at least 3 times thinner Cr2O3 scale thickness compared to uncoated steel. The coated steel samples showed lower area-specific resistance (ASR) values than the uncoated steel after 3000\ua0h of exposure, irrespective of the coating thickness, composition and deposition method