Dynamic Changes in LSM Nanoparticles on YSZ: A Model System for Non-Stationary SOFC Cathode Behavior

The interaction between nanoparticles of strontium-doped lanthanum manganite (LSM) and single-crystal yttria-stabilized zirconia (YSZ) was investigated using atomic force microscopy, X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM)/energy-dispersive X-ray spectroscopy (EDX). Nanoparticles of LSM were deposited directly onto single-crystal YSZ (100) substrates using an ultrasonic spray nozzle. As samples were annealed from 850 to 1250 degrees C, nanoparticles gradually decreased in height and eventually disappeared completely. Subsequent reduction in H-2/H2O at 700 degrees C resulted in the reappearance of nanoparticles. Studies were carried out on identical regions of the sample, allowing the same nanoparticles to be characterized at different temperatures. Morphological changes indicate the formation of a thin layer of LSM, and XPS results support the observation by indicating an increase in signal from the La and Sr and a decrease in signal from the Y and Zr with increasing temperature. SEM/EDX was used to verify that the nanoparticles in the reduced sample contained La. The changes in the LSM/YSZ morphology may be important in explaining the nonstationary behavior observed in operating solid-oxide fuel cells (SOFCs). The thin layer of LSM initially results in poor cathode performance; reducing conditions then lead to film disruptions, indicating nano/microporosity, that increase oxygen ion diffusion and performance. (C) 2009 The Electrochemical Society. [DOI: 10.1149/1.3095516] All rights reserved.