MANGANITE-ZIRCONIA COMPOSITE CATHODES FOR SOFC - INFLUENCE OF STRUCTURE AND COMPOSITION

The performance of La(0.85)Sr(0.15)Mn(y)O3(+/-delta) (LSM(y)) as catho de material For Solid Oxide Fuel Cells (SOFC) operating at 1000 degree s C and p(O2) = 0.21 atm. can be improved by increasing the Triple Pha se Boundary Length (TPBL) where the gas, the electrode and the electro lyte are in contact and by preventing the formation of highly resistiv e (Zr, La)-rich layers at the electrode/electrolyte interface. In the present work, the influence of three parameters on the performance of LSM(y) cathodes has been investigated: the adhesion of the cathode to the electrolyte, the addition of Y2O3-stabilized ZrO2 (YSZ) to the cat hode and the excess of Mn (LSM(1.1)). The electrode resistance has bee n measured by impedance spectroscopy at 1000 degrees C, p(O2) = 0.21 a tm and equilibrium potential. The interface structure and the reaction s between the electrode and the electrolyte have been examined by Scan ning Electron Microscopy and Transmission Electron Microscopy combined with Energy Dispersive X-ray Spectrometry. The results obtained indic ate that the reaction resistance of the cathode for the oxygen reducti on process decreases upon increasing the TPBL. Furthermore, the format ion of highly resistive (Zr, La)-rich layers at the interface electrod e/electrolyte can be prevented by increasing the Mn-content in the LSM (y), the amount of Mn necessary being dependent of the amount of YSZ i n the cathode.