Sealant, SOFC stack

In addition to the YSZ electrolyte and metallic interconnect, SOFC stack also includes component materials such as seals and manifolds. Sealant materials based on glass or... 

N. Lahl et al. Aluminosilicate Glass Ceramics as Sealant in SOFC Stacks, Solid Oxide Fuel Cells Vol. VI, Electrochemical Society Proceedings Vol. 99-19, pp. 1057-1066. 

Interestingly, research has started on single chamber SOFC (SC-SOFC) concepts. However, the SC-SOFC exhibits inherently low power density and is therefore primarily of academic interest. It has the potential to relax cell component requirements and probably to ease manufacture. The principle of SC-SOFC is that it is fed by an air fuel mixture which flows onto the PEN contained in a single compartment, avoiding the use of gas separator plates and high temperature sealants. The fluid may flow simultaneously or sequentially along the electrodes. Both electrodes are either built onto the same side of the electrolyte some distance apart or on opposite sides. Low temperature operation would apparently suppress direct combustion of the air fuel mixture provided the electrode materials chosen are highly selective towards their respective catalytic reactions. SC-SOFC stacks may hold prospects in specific applications where the reaction products are the prime focus. 

V.A.C. Haanappel, V. Shemet, S.M. Gross, et al., Behaviour of various glass-ceramic sealants with ferritic steels under simulated SOFC stack conditions. Journal of Power Sources, 150 (2005) 86-100. 

Shemet, V., Vinke, I.C., and Steinbrech, R.W. (2006) Chemical interaction between glass—ceramic sealants and interconnect steels in SOFC stacks. 

Haanappel VAC, Shemet V, Vinke IC, Gross SM, Koppitz Th, Menzler N, Zahid M, Quadakkers WJ (2005) Evaluation of the suitability of various glass sealant-alloy combinations under SOFC stack conditions. J Mater Sci 40 1583-1592... 

Hannappel, V.A.C., Shemet, V, Vinke, I.C. and Quadakkers, W.J. (2005), A novel method to evaluate the suitability of glass sealant-alloy combinations under SOFC stack conditions, J. Power Sources., 141, 102-107. 

Fig. 1 Examples of mechanical failures and microstructural alterations observed in SOFC stacks, a Delamination of cathode current collection layer [21], reproduced here with kind permission from ASME 2008. b cracking of the sealant [10], reproduced here with kind permission from Elsevier 2006, and loss of gas-tighntess [72], reproduced here with kind permission from John Wiley and Sons 2009. c MIC coating delamination [18], reproduced here with kind permission from Elsevier 2008. d anode support reoxidation cycling [25], reproduced here with kind permission from Elsevier 2009 e formation of zirconates in LSM-YSZ cathode [68], reproduced here with kind permission from Elsevier 2009. f chromium deposit in LSM-YSZ cathode [78], reproduced here with kind permission from The Electrochemical Society 2007...

Summarizing progress in the field thus far, the book describes current materials, future advances in materials, and significant technical problems that remain unresolved. The first three chapters explore materials for the electrochemical cell electrolytes, anodes, and cathodes. The next two chapters discuss interconnects and sealants, which are two supporting components of the fuel cell stack. The final chapter addresses the various issues involved in materials processing for SOFC applications, such as the microstructure of the component layers and the processing methods used to fabricate the microstructure. 

Planar SOFC, in particular, monolithic designs (MHI) are capable of high (volumetric) power densities most favoured by direct and short current paths across the stack components. The PEN is principally square, rectangular and circular (Ceramic Fuel Cells Limited (CFCL), Mitsubishi Materials Corp., SulzerHexis) in shape with active surface areas of 100-200 cm2 (15.5-31 in2). A drawback of this design is that it often necessitates the use of high temperature sealants for application at the in-... 

It must be taken into account that silica contamination in the SOFC does not only originate from a contamination of the fuel stream but silicon compounds can be also contained in the water used for the steam reformer upstream of the SOFC or can derive from stack sealants. 

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