Importance of thermochemical studies of the SOFC materials for the stack modelling

Mirosław Miller 

Wrocław University of Technology, Wybrzeże Wyspiańskiego, Wrocław 50-370, Poland

Abstract

Materials used as the SOFC components are complex oxide phases or metal/metal oxide composites which are expected to be stable under the operation conditions of the stack. Under “stable phase” is meant, that: (a) its chemical composition and crystal structure remains unchanged upon long-term operating conditions of the stack, (b) no reactions occur at the interfaces of different phases being in the direct contact, (c) no crystal structure change takes place upon heating / cooling the phase between room and operating temperature of SOFC, and (d) no vaporisation processes occur at operating temperature and atmosphere. Considering the high operating temperature of SOFC and the gradient of the O2- partial pressure between the cathode (0.2 bar) and anode side (10-19 bar), no strictly “stable” metal oxide phases exist. For this reason, thermochemical studies as reactivity, vaporisation, phase relations, and diffusion of the SOFC components are of big importance for modelling the stacks and for better understanding the degradation processes going on in the operating SOFCs.

In the present work phase diagram and vaporisation studies of lanthanum chromite (LaCrO3) and lanthanum gallate (LaGaO3) doped with the two-valent ions (Mg, Ca, Sr) are presented. Both materials show the perovskite structure and are commonly in use in the today SOFC technology. Phase relations in the 8YSZ - LaMnO3 system (8YSZ = 8 mol% Y2O3 / 92 mol% ZrO2 solid solutions) are presented as well. Results are discussed from the point of view of the possible degradation processes in SOFCs. Studies presented were performed by the Author by using the XRD, EDX/SEM, and KEMS (Knudsen Effusion Mass Spectrometry) methods. The latter method is described more detailed in the present work as still non-conventional method used in the high temperature thermochemical investigations.

 

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Presentation: oral at E-MRS Fall Meeting 2005, Symposium E, by Mirosław Miller
See On-line Journal of E-MRS Fall Meeting 2005

Submitted: 2005-06-06 08:10
Revised:   2009-06-07 00:44