Crystal-Orientation-Dependent Oxygen Exchange Kinetics on Mixed Conducting Thin-Film Surfaces Investigated by In Situ Studies

Matthäus Siebenhofer; Christoph Riedl; Andreas Nenning; Sergej Raznjevic; Felix Fellner; Werner Artner; Zaoli Zhang; Christoph Rameshan; Jürgen Fleig; Markus Kubicek

doi:10.1021/acsaem.3c00870

Crystal-Orientation-Dependent Oxygen Exchange Kinetics on Mixed Conducting Thin-Film Surfaces Investigated by In Situ Studies

ACS Appl Energy Mater. 2023 Jun 13;6(12):6712-6720. doi: 10.1021/acsaem.3c00870. eCollection 2023 Jun 26.

Authors

Affiliations

¹ Institute of Chemical Technologies and Analytics, Vienna University of Technology, Vienna 1060, Austria.
² Centre for Electrochemistry and Surface Technology (CEST), Wiener Neustadt 2700, Austria.
³ Erich Schmid Institute of Materials Science, Austrian Academy of Sciences, Leoben 8700, Austria.
⁴ X-Ray Center, Vienna University of Technology, Vienna 1060, Austria.
⁵ Chair of Physical Chemistry, Montanuniversität Leoben, Leoben 8700, Austria.

Abstract

The oxygen exchange kinetics and the surface chemistry of epitaxially grown, dense La_0.6Sr_0.4CoO_3-δ (LSC) thin films in three different orientations, (001), (110), and (111), were investigated by means of in situ impedance 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 in ex situ measurement 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.