Improving the interface adherence at sealings in solid oxide cell stacks

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FOCUS ISSUE

INTERCONNECTS AND INTERFACES IN ENERGY CONVERSION MATERIALS

Improving the interface adherence at sealings in solid oxide cell stacks Ilaria Ritucci1,a) , Ragnar Kiebach1, Belma Talic1, Li Han1, Philipp Zielke1, Peter V. Hendriksen1, Henrik L. Frandsen1 1

Department of Energy Conversion and Storage, Technical University of Denmark, DK-4000 Roskilde, Denmark Address all correspondence to this author. e-mail: [email protected]

a)

Received: 19 September 2018; accepted: 14 November 2018

Thermal cycling of planar solid oxide cell (SOC) stacks can lead to failure due to thermal stresses arising from differences in thermal expansion of the stack’s materials. The interfaces between the cell, interconnect, and sealing are particularly critical. Hence, understanding possible failure mechanisms at the interfaces and developing robust sealing concepts are important for stack reliability. In this work, the mechanical performance of interfaces in the sealing region of SOC stacks is studied. Joints comprising Crofer22APU (preoxidized or coated with MnCo2O4 or Al2O3) are sealed using V11 glass. The fracture energy of the joints is measured, and the fractured interfaces are analyzed using microscopy. The results show that choosing the right coating solution would increase the fracture energy of the sealing area by more than 70%. We demonstrate that the test methodology could also be used to test the adhesion of thin coatings on metallic substrates.

Introduction Solid oxide fuel cells (SOFC) are electrochemical devices that can efficiently convert fuels such as hydrogen and gaseous hydrocarbons into electricity [1, 2, 3]. If operated in the electrolysis mode (SOEC), they can be used to produce hydrogen or syngas, which can be stored or converted into liquid fuels for transportation [4, 5, 6, 7]. To advance the commercialization of solid oxide cell (SOC) technology, production and material costs need to be further decreased and long-term stability/reliability demonstrated [8]. Designing SOC stacks requires a careful selection of materials to provide the chemical and mechanical stability needed for several thousand hours of operation and to ensure robustness against thermal cycling. In this context, the sealings represent a critical issue, especially for planar SOC technology. Thermal mismatches between the sealing material and other stack components (e.g., interconnects and cells) can lead to delamination at the interfaces or formation of cracks inside the sealant, which may give rise to mixing of the fuel and the oxidant and, in worst case, lead to stack failure [9, 10, 11]. An ideal sealant for SOC stacks should adhere well to the joining components, remain chemically stable over time, provide high mechanical strength, have a low cost, provide

ª Materials Research Society 2019

electrical insulation, and have a coefficient of thermal expansion (CTE) that matches well with those of the other stack components [12, 13, 14]. Today, three main types of sealing materials are considered for SOC application: (i) compressive se