film electrodes of thickness 100, 450, 650, and 700 nm were fabricated on yttria-stabilized zirconia ͑YSZ͒ 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 ⍀ cm 2 was measured for the La surface-doped 650 nm thick electrode at 250 mA/cm 2 .
La0.8Sr0.2MnO3-δ (LSM) film electrodes of thickness 100-700 nm were deposited onto yttria-stabilized zirconia (YSZ) and cerium gadolinium oxide (CGO) electrolyte pellets by ultrasonic spray pyrolysis. The activation behavior upon initial application of cathodic polarization was studied with respect to the magnitude of applied potential and current, duration of applied potential, and surface doping with Sr, La and Mn oxides or La0.6Sr0.4FeO3 (LSF) nanoparticles. We provide evidence for two separate activation phenomena - a surface dominated process during short-term application, and bulk pore formation during long-term application of cathodic current.
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