Post-experimental analysis of a solid oxide fuel cell stack using hybrid seals

Abstract

h i g h l i g h t sPost-experimental analysis of a SOFC stack after 1800 h of operation. Microstructural analysis of the glass-coated hybrid seal. Materials interactions between glass-coated seals and Crofer 22 APU interconnects. Dual exposure of 0.2 mm thin Crofer 22 APU plates in stack operating conditions. a b s t r a c t A post-experimental analysis of a SOFC stack is presented. The stack was operated for 1800 h at 700 C with air and hydrogen and contained hybrid glass-Thermiculite 866 seals. The goal of this work was to investigate the sealing microstructure and possible corrosion during mid-term operation. It was found that hybrid seals could effectively compensate for manufacturing tolerances of cells and other components due to the compliance of the glass layer. Additionally, different interfaces were investigated for corrosion. Corrosion was not observed at two-phase interfaces such as Crofer 22 APU/glass, glass/electrolyte and glass/Thermiculite 866. The three-phase interface between Crofer 22 APU/glass/hydrogen exhibited no corrosion. Some evidence of non-systematic corrosion was found at the Crofer 22 APU/ glass/air interface. The possible reasons for the corrosion are discussed. Lastly, dual exposure to humid hydrogen and air of the 0.2 mm Crofer 22 APU interconnect had no detrimental effect on the corrosion compared to air exposure. Overall the hybrid seals used in combination with the thin interconnects were found to be a promising solution due to the low leak rate and limited material interactions.

Ageing of Materials at Inlet and Outlet Fuel Manifolds in a SOFC Stack

“…Opila (33), Mn rich volatile compounds can form and this would be coherent with the previously observed Mn enrichment of the GS at the outlet. Similar features are presented in a recently published paper on operated stack (16).…”

“…Comparing the results inlet and outlet gathered from segment 1 (exposed to the fuel stream) of layer 1, it is possible to observe that at the outlet the percentage of small sized pores (< 5 µm 2 ) is higher (f% > 30%). For both inlet and outlet this effect can be connected with the exposure to a stream, which may trigger the formation of volatile compounds (16,(23)(24)(25). The higher frequency found at the outlet layers is coherent with the high amount of water vapor present in the exhaust fuel stream increasing the reactivity of GS and the formation of volatile compounds rich in elements like Ca and B.…”

“…The latter could be formed during shear stress at high temperature (i.e. when the viscosity of the GS is lower, 6-7), the devitrification process (1) or the evaporation of elements from the matrix due to the interaction with the atmosphere (16,23). The found porosity is rather high when compared to the typical data found in literature.…”

“…The interaction between materials (sealant-metal combination, sealant-electrolyte combination, or just sealant or metal, with single and dual atmosphere) has been object of several studies which pointed out the delicate role played by the structural parts in the reliability of the stack and its efficiency (5,(10)(11)(12)(13). In those previous studies, various kinds of sealing materials have been successfully used: ceramic fiber reinforced glass (1), borosilicate glasses (1), glass-ceramic evolving into a rigid or semi-rigid glass-ceramic mixture by specific thermal treatment (1,14,15), and combinations of them (5,16,17). Several studies have been made on materials aged in situ (10-13, 16, 18-22) under various atmospheres and working conditions.…”

Progress and prospects of reversible solid oxide fuel cell materials

“…For structural components such as electrode supports, they should have a certain strength and thermal shock resistance, easy to process, and the cost is as low as possible. Besides the attention of cell materials, other materials in the cell (stack) also need attention, including the direct interconnection of the series cell (Shao and Tade ´, 2016) and the current collection layer (Shen and Zhang, 2020) and the sealing material (Thomann et al, 2015).…”