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 cathode material For Solid Oxide Fuel Cells (SOFC) operating at 1000 degrees C and p(O2) = 0.21 atm. can be improved by increasing the Triple Phase Boundary Length (TPBL) where the gas, the electrode and the electrolyte are in contact and by preventing the formation of highly resistive (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 cathode and the excess of Mn (LSM(1.1)). The electrode resistance has been measured by impedance spectroscopy at 1000 degrees C, p(O2) = 0.21 atm and equilibrium potential. The interface structure and the reactions between the electrode and the electrolyte have been examined by Scanning Electron Microscopy and Transmission Electron Microscopy combined with Energy Dispersive X-ray Spectrometry. The results obtained indicate that the reaction resistance of the cathode for the oxygen reduction process decreases upon increasing the TPBL. Furthermore, the formation of highly resistive (Zr, La)-rich layers at the interface electrode/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 in the cathode.