Impact of the Oxygen Vacancies of the LSCF (La0.6Sr0.4Co0.2Fe0.8O3–δ) Perovskite on the Activation Energy of the Oxygen Reduction/Evolution Reaction

La0.6Sr0.4Co0.2Fe0.8O3–δ (LSCF) perovskites, in the form of in–house electrospun nanofibers and commercial powders, have been tested through synchrotron x–ray diffraction and electrochemical impedance spectroscopy in the 800–1200 K range. The former analyses make it possible to evaluate the oxygen vacancies (OV) concentration, and the latter allows to assess the electrokinetics of the oxygen reduction/evolution reaction. Equivalent circuit modeling is carried out to identify the basic electrochemical processes and evaluate the associated polarization resistance Rp. One high-frequency process and two intermediate-frequency processes are recognized. For all electrochemical processes, OV concentration and Rp behave similarly with temperature in both nanofiber and granular electrodes. This led to the proposal of a new equation. For each electrochemical process, it was shown that the activation energy is the sum of an intrinsic electrochemical activation energy, plus the formation energy of OVs. For the LSCF perovskites tested in this work, the intrinsic electrochemical activation energy was found to be independent of the preparation procedure and crystal structure. In contrast, the OV formation energy was found to be strongly dependent on the preparation procedure and crystal structure, with values ranging between 0.5 and 24.1 kJ mol−1. A complete set of data is provided, which can be useful for future simulation studies.