Interface reactions during co-firing of solid oxide fuel cell components

When all the cell components are fired at a single step, better performance is expected as the interfaces between the adjacent components not only provide better adhesion, but also offer good morphological features and properties. The present investigation is an attempt towards fabrication of such types of cells. A new cathode composition, LaNi0.6Fe0.4O3 (LNF), is used instead of conventional La(Sr)MnO3 (LSM). However, following a co-deposition and single-step firing, unit cells with LNF cathode produce no voltage output when electrochemical tests are performed. The reason for this adverse result was analyzed and the microstructural analyses showed a thick white gas-tight film at the interface between the zirconia (electrolyte) and LSM-YSZ (cathode). This white layer starts forming at ∼1300 °C and becomes thicker and thicker as the sintering temperature increases. Samples co-fired at 1400 °C for 5 h yield a white layer of thickness ∼2 μm. Quantitative EDX and XRD analysis confirmed the formation of the La2Zr2O7 reaction phase which is the reason for such poor performance. LNF could have emerged as the SOFC cathode material of choice because of its favorable properties, but it is problematic when fabricated along with other cell components (as in the presentation investigation).