The oxygen exchange kinetics and the surface chemistry
of epitaxially
grown, dense La0.6Sr0.4CoO3−δ(LSC) thin films in three different orientations, (001), (110),
and (111), were investigated by means ofin situimpedance
spectroscopy during pulsed laser deposition (i-PLD) and near-ambient-pressure
X-ray photoelectron spectroscopy (NAP-XPS). i-PLD measurements showed
that pristine LSC surfaces exhibit very fast surface exchange kinetics
but revealed no significant differences between the specific orientations.
However, as soon as the surfaces were in contact with acidic, gaseous
impurities, such as S-containing compounds in nominally pure measurement
atmospheres, NAP-XPS measurements revealed that the (001) orientation
is substantially more susceptible to the formation of sulfate adsorbates
and a concomitant performance decrease. This result is further substantiated
by a stronger increase of the work function on (001)-oriented LSC
surfaces upon sulfate adsorbate formation and by a faster performance
degradation of these surfaces inex situmeasurement
setups. This phenomenon has potentially gone unnoticed in the discussion
of the interplay between the crystal orientation and the oxygen exchange
kinetics and might have far-reaching implications for real solid oxide
cell electrodes, where porous materials exhibit a wide variety of
differently oriented and reconstructed surfaces.