Characterisation and Evaluation of Compression Loaded Sealing Concepts for SOFC Stacks

Glass-ceramics are well-established seals for solid oxide fuel cell (SOFC) stacks. Due to disadvantages like inherent brittleness, alternative sealing concepts are of increasing interest. Promising candidates are metallic seals, mica, ceramic fiber sheets, and combinations thereof. However, unlike glass ceramics, these concepts require permanent sealing loads. The present work focuses on characterization and concept evaluation of the alternative seals with regard to their sealing capability, required load, plastic deformation, and elastic recovery. All experiments were conducted at the operating temperature of SOFC stacks (800°C) in air. In the case of metallic seals, an insulating interlayer is a prerequisite to avoid short circuiting during stack operation. Thus it was also examined whether pre-oxidation of the metallic seals via alumina scale formation on the ferritic steals provides electrical insulation without loss of gas tightness. Application potential of alternative sealants in SOFC stacks is discussed.