Surface Chemistry and Degradation Processes of Dense La_0.6Sr_0.4CoO_3−δ Thin Film Electrodes

Abstract The changes of the surface morphology and the surface chemistry of LSC thin films grown on different substrates were tracked for 100 hours in solid oxide fuel cell operating temperature and atmosphere. Atomic force microscopy was used to monitor the formation of particles at the LSC surface. Depending on the thin film structure (polycrystalline vs. epitaxial), different particle formation dynamics were observed. Electron microscopy was employed to investigate the chemistry of the segregated particles and revealed that the particles were Sr- and S-rich. Secondary ion mass spectrometry and X-ray photoelectron spectroscopy measurements on degraded LSC thin films also found significant amounts of sulphur on the LSC surface, despite no deliberate addition of sulphur compounds, as well as A-site cation enrichment. Impedance spectroscopy was used to track the polarization resistance of LSC grown on YSZ over the same degradation period and a strong increase of the polarization resistance and of its activation energy was revealed (1.09-1.73 eV). The experimental results indicate that sulphur adsorption on LSC surfaces is omnipresent in the investigated conditions and even trace amounts of sulphur compounds present in nominally pure measurement gases account for particle formation and multiple degradation effects under operating conditions.