[Back]

E. Povoden-Karadeniz:
"Thermodynamic modeling of materials for solid oxide fuel cells";
Talk: Seminar des Instituts für Werkstoffwissenschaft und Werkstofftechnologie, TU Wien, Zemanek-Sem.Raum; 2009-02-11.

Chromium-containing metallic interconnects are commonly used in planar-design solid oxide fuel cells (SOFC) due to their high oxidation resistance, thermal stability, mechanical strength, good electronic and negligible ionic conductivity, and low fabrication costs. However high-valent gaseous Cr-oxide and chromium-oxyhydrides can diffuse under fuel-cell operation conditions from the interconnect into the cathode up to the cathode-electrolyte interface, where they cause the degradation of the cell by detrimentally affecting the O2 adsorbtion, reduction, and diffusion process, associated to the formation of Cr-Mn spinel and Cr2O3.

Sr-doped lanthanum manganite (LSM) with the perovskite structure ABO3-dis used as cathode materials in SOFC. A thermodynamic La-Sr-Mn-Cr-O oxide database is highly desirable for the development of endurable SOFC: thermodynamic calculations set an important base for the optimization of cathodes aiming to avoid long-term degradation due to chromium poisoning. The database should meet the demand to calculate stable and metastable phase equilibria, thermodynamic driving forces and activities, as well as defect concentrations of the cathode contaminated by Cr at different temperatures and oxygen partial pressures. These requirements are conformed by using the CALPHAD approach.

Using the new thermodynamic database for testing equilibrium conditions in a Sr-doped lanthanum manganite cathode (LSM) affected by chromium, it is concluded that at the cathode/electrolyte interface of a Cr-"poisoned" cell Cr-Mn spinel exists in thermodynamic equilibrium with LSM, whereas Cr2O3 is metastable. It is shown that the interaction of chromium with the LSM cathode leads to a change of the defect chemistry of the perovskite phase. In particular the concentrations of cation and oxygen vacancies are smaller than in an LSM without chromium.

http://publik.tuwien.ac.at/files/PubDat_183992.pdf