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Improved interconnect materials for next-generation Solid Oxide Fuel Cells
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
2019 (English)Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
Abstract [en]

Solid Oxide Fuel Cells (SOFC) are attractive candidates in the search for cleaner and energy efficient production due to their numerous advantages such as fuel flexibility, modularity and exceptional efficiencies when combined heat and power is harnessed. A key element in its design are the interconnects which are mainly manufactured from custom ferritic stainless steels to carry the electricity between two adjacent cells. However, the high operation temperatures increase the chromia scale thickness in those steels, which reduces their conductivity. At the same time, chromium (VI) volatilization due to the wet atmosphere poisons the electrodes and reduces the cell life. Therefore, the narrow of the selection of suitable materials and high production costs have hindered their commercialization. Recent advances in lower temperature SOFC operation have opened a window for new interconnect materials and innovative processes. A Ce/Co nanocoating can be applied in the readily available AISI 441 ferritic steel to form a protective spinel oxide layer that reduces the effect of both degradations in the interconnects. The coating is applied in a continuous roll-to-roll process and then the interconnect shape is pressed in the material, manufactured as Sanergy HT 441 by Sandvik. However, mechanical stresses cause microcracks that expose the substrate material, which can impact the oxidation behaviour negatively. Fortunately, pre-treatments can achieve the spinel to diffuse over short distances and combine with elements in the substrate, homogenizing the protective effect. This phenomenon known as self-healing has not been studied with sufficient depth for the Sanergy HT 441. Thus, different series of temperature and short pre-treatments times were tested, and self-healing properties were observed by means of SEM surface characterization and chemical analysis. The results indicate that self-healing can be obtained within short times using isothermal pre-treatments at temperatures over 750 °C.

Abstract [sv]

Solid Oxide Fuel Cells (SOFC) är attraktiva kandidater i jakten på renare och energieffektiv produktion på grund av deras många fördelar som bränsleflexibilitet, modularitet och exceptionella effektivitet när kombinerad värme och kraft utnyttjas. Ett viktigt element i dess utformning är sammankopplingar som huvudsakligen tillverkas av anpassade ferritiska rostfria stål för att transportera elektricitet mellan två angränsande celler. De höga driftstemperaturerna ökar emellertid tjockleken på kromskalan i dessa stål, vilket minskar deras konduktivitet. Samtidigt förorenar krom (VI) på grund av den våta atmosfären elektroderna och reducerar celllivslängden. Därför har det smala urvalet av lämpliga material och höga produktionskostnader hindrat deras kommersialisering. De senaste framstegen inom SOFC-drift med lägre temperatur har öppnat ett fönster för nya sammankopplingsmaterial och innovativa processer. En Ce / Co-nanocoating kan appliceras i det lättillgängliga AISI 441 ferritstålet för att bilda ett skyddande spinelloxidskikt som minskar effekten av båda nedbrytningarna i sammankopplingarna. Beläggningen appliceras i en kontinuerlig rulle-till-rullningsprocess och sedan pressas sammankopplingsformen in i materialet, tillverkat som Sanergy HT 441 av Sandvik. Mekaniska spänningar orsakar emellertid mikrokrackar som exponerar underlagsmaterialet, vilket kan påverka oxidationsbeteendet negativt.Lyckligtvis kan förbehandlingar uppnå att spinellen diffunderar över korta avstånd och kombineras med element i underlaget och homogeniserar den skyddande effekten. Detta fenomen som kallas självhelande har inte studerats med tillräckligt djup för Sanergy HT 441. Således testades olika serier av temperatur och korta förbehandlingstider, och självhelande egenskaper observerades med hjälp av SEM-ytkarakterisering och kemisk analys. Resultaten indikerar att självläkning kan uppnås inom korta tider med användning av isotermisk förbehandling vid temperaturer över 750 ° C.

Place, publisher, year, edition, pages
2019. , p. 60
Series
TRITA-ITM-EX ; 2019:580
Keywords [en]
Solid Oxide Fuel Cells, High Temperature Corrosion, Self-healing, Interconnects
National Category
Materials Engineering
Identifiers
URN: urn:nbn:se:kth:diva-259656OAI: oai:DiVA.org:kth-259656DiVA, id: diva2:1352782
External cooperation
Sandvik AB
Educational program
Master of Science - Engineering Materials Science
Presentation
2019-09-04, Sefström, Brinellvägen 23, Bergs, våningsplan 1, KTH Campus, Stockholm, 16:34 (English)
Supervisors
Examiners
Available from: 2019-09-24 Created: 2019-09-19 Last updated: 2019-09-24Bibliographically approved

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