La0.6Sr0.4FeO3-d (LSF64) is a mixed ionic electronic conductor with a potential use as electrode material in solid oxide fuel and electrolysis cells. Due to its comparatively high thermo-chemical stability over a wide oxygen partial range, it can not only be used under oxidizing, but also under reducing conditions. In this thesis the impact of oxidizing and reducing atmospheres on LSF64 was characterized using well-defined electrodes in impedance spectroscopy, oxygen isotope exchange and subsequent time-of-flight secondary ion mass spectrometry (TOF-SIMS) as well as high temperature in-situ powder X-ray diffraction (XRD). Impedance spectra of well-defined thin film LSF64 microelectrodes revealed an electronic sheet resistance under reducing conditions. However, this sheet resistance can be overcome by the use of an additional current collector. In analogy to Ni=YSZ cermet, the ion conducting LSF64 is combined with an electronic conducting current collector. In this work well-defined platinum current collector structures were applied. Different geometries of current collectors as well as their positioning on top and beneath the film are discussed. Astonishingly, with the sheet resistance being compensated the electrode resistance and accordingly the oxygen exchange kinetics, is similar in both atmospheres. In air rather fast degradation of the electrochemical activity is found. Impedance measurements under cyclic gas change on micro- as well as macroscopic electrodes show that the gas change to reducing atmosphere can regenerate the surface to a state of higher oxygen exchange kinetics, i.e. H2=H2O can annihilate the previous degradation in air. The chemical capacitance, from the measured thin-film electrodes, is in good accordance with that calculated from the defect model, using the relationship between oxygen partial pressure (pO2 ) and oxygen non-stoichiometry (d) as found in literature. Despite the high thermo-chemical stability of LSF64, all electrodes show a long-term degradation in surface kinetics. The degradation was investigated by additional in-situ high temperature X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) measurements. XRD on LSF64 powder was performed under different atmospheres with temperatures up to 800C. The diffraction patterns show decomposition in dry hydrogen and the formation of a small amount of secondary phases under reducing conditions: iron oxides and Ruddlesden-Popper phases. XPS measurements on LSF64 thin films on yttria stabilized zirconia (YSZ) suggest a slight enrichment of strontium towards the surface. Oxygen isotope exchange confirmed the findings from the electrochemical measurements, namely that the oxygen exchange kinetics is similar under oxidizing and reducing conditions. The oxygen diffusivity was found to be higher under reducing conditions, which is to be expected due to a higher concentration of oxygen vacancies.