Abstract
The oxygen exchange and diffusion properties of La0.6Sr0.4CoO3 − δ thin films on yttria stabilized zirconia were analyzed by impedance spectroscopy and 18O tracer experiments. The investigations were performed on the same thin film samples and at the same temperature (400 °C) in order to get complementary information by the two methods. Electrochemical impedance spectroscopy can reveal resistive and capacitive contributions of such systems, but an exact interpretation of the spectra of complex oxide electrodes is often difficult from impedance data alone. It is shown that additional isotope exchange depth profiling can significantly help interpreting impedance spectra by giving reliable information on the individual contribution and exact location of resistances (surface, electrode bulk, interface). The measurements also allowed quantitative comparison of electrode polarization resistances obtained by different methods.
Highlights
Mixed ionic and electronic conducting (MIEC) oxides are promising materials for electrochemical devices based on gas–solid interactions such as solid oxide fuel cells (SOFCs), gas sensors, or permeation membranes [1,2,3,4]
X-ray diffraction (XRD) measurements were performed in parallel beam geometry on a D8-Discover instrument (Bruker AXS) which was equipped with a General Area Detection Diffraction System (GADDS)
In oxygen tracer experiments, it could be unambiguously shown that the oxygen exchange at the surface is rate limiting and the best suited model for impedance analysis could be identified
Summary
Mixed ionic and electronic conducting (MIEC) oxides are promising materials for electrochemical devices based on gas–solid interactions such as solid oxide fuel cells (SOFCs), gas sensors, or permeation membranes [1,2,3,4]. Several analytical methods exist to investigate the catalytic activity of MIEC electrodes towards the oxygen reduction reaction (ORR) with two of the most important approaches being electrochemical impedance spectroscopy (EIS) and 18O isotope exchange depth profiling (IEDP). EIS yields information on resistive and capacitive contributions of MIEC electrodes on ionic conducting substrates Many properties such as the catalytic activity of surfaces, oxygen nonstoichiometry, chemical diffusion, conductivities, transport reactions across solid|solid phase boundaries, or the formation of impurity phases can be indirectly probed. While impedance spectroscopy is a quite common method to investigate mixed conducting thin film electrodes, [6,10,11,12] oxygen tracer experiments are often performed on bulk samples [13,14,15,16]. Quantitative material parameters are deduced from both types of experiments and comparison of the data allowed testing the appropriateness of analysis models
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