Performance and activation behavior of surface-doped thin-film La0.8Sr0.2MnO3-delta cathodes

La0.8Sr0.2MnO3-delta (LSM) film electrodes of thickness 100, 450, 650, and 700 nm were fabricated on yttria-stabilized zirconia (YSZ) electrolyte pellets by ultrasonic spray pyrolysis. In addition, 650 nm thick LSM electrodes with a surface doped with La-, Sr-, or Mn-nitrate were studied. Electrodes were deposited on both sides of the YSZ pellets in a symmetric arrangement. The individual electrode impedance spectra were measured at 973 K in laboratory air using a reference electrode placed on the free electrolyte surface. The open-circuit polarization resistance of the pure LSM and Sr and Mn surface-doped electrodes decreased significantly after initial application of cathodic current. In contrast, the La- doped sample showed no activation, with an initial polarization resistance similar to the activated, undoped LSM film. This indicates that surface La species play an important role in LSM electrode activation. All of the electrodes showed a strong, nonlinear decrease in polarization resistance accompanied by a linear decrease in ohmic resistance with increasing applied cathodic current. These changes are attributed to the introduction of a bulk-ion-transport path in the LSM film due to reduction of LSM under polarization. A minimum polarization resistance of 0.17 Omega cm(2) was measured for the La surface-doped 650 nm thick electrode at 250 mA/cm(2). (c) 2007 The Electrochemical Society.