The research and development of new Solid Oxide Fuel Cell cathode materials is an area of intense activity. The kinetic coefficients describing the O2-reduction mechanism are the O-ion diffusion ( D chem ) and the O-surface exchange coefficients ( k chem ). These parameters are strongly dependent on the nature of the material, both on its bulk and surface atomic and electronic structures. This review discusses the method for obtaining the kinetic coefficients through the combination of electrochemical impedance spectroscopy with focused ion-beam 3D tomography measurements on porous electrodes (3DT-EIS). The data, together with oxygen non-stoichiometry thermodynamic data, is analysed using the Adler-Lane-Steele model for macro-homogeneous porous electrodes. The results for different families of oxides are compared: single- and double-layered perovskites with O-vacancies defects, based on La-Sr cobalt ferrites (La0.6Sr0.4Co1-xFexO3-δ , x = 0.2 and 0.8) and La/Pr-Ba cobaltites (La0.5-xPrxBa0.5CoO3-δ , x = 0.0, 0.2 and 0.5), as well as Ruddlesden-Popper nickelates (Nd2NiO4 +δ ) with O-interstitial defects. The analysis of the evolution of molar surface exchange rates with oxygen partial pressure provides information about the mechanisms limiting the O2-surface reaction, which generally is dissociative adsorption or dissociation-limited. At 700 °C in air, the La-Ba cobaltite structures, La0.5-xPrxBa0.5CoO3-δ , feature the most active surfaces ( k chem ≃0.5–1 10−2 cm.s−1), followed by the nickelate Nd2NiO4 +δ and the La-Sr cobalt ferrites, with k chem ≃1–5 10−5 cm.s−1. The diffusion coefficients D chem are higher for cubic perovskites than for the layered ones. For La0.6Sr0.4Co0.8Fe0.2O3-δ and La0.6Sr0.4Co0.2Fe0.8O3-δ , D chem is 2.6 10−6 cm2.s−1 and 5.4 10−7 cm2.s−1, respectively. These values are comparable to D chem = 1.2 10−6 cm2.s−1, observed for La0.5Ba0.5CoO3-δ . The layered structure drastically reduces the O-ion bulk diffusion, e.g. D chem = 1.3 10−8 cm2.s−1 for the Pr0.5Ba0.5CoO3-δ double perovskite and D chem ≃2 10−7cm2.s−1 for Nd2NiO4 +δ . Finally, the analysis of the time evolution of the electrodes shows that the surface cation segregation affects both the O-ion bulk diffusion and the surface exchange rates.

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A‐site cationic ordered LaBaCo2O6−δ and disordered La0.5Ba0.5CoO3−δ perovskite phases were obtained by solid state reaction. Their structural properties were studied at room temperature and 673 K, by combining powder diffraction techniques, X‐ray diffraction and neutron powder diffraction with an independent determination of the oxygen content of the samples by thermogravimetry. La0.5Ba0.5CoO3−δ exhibits cubic symmetry with cations randomly distributed, whereas LaBaCo2O6−δ shows tetragonal symmetry with the La3+ and Ba2+ ions distributed in alternating layers. The diffraction data were analyzed using the Rietveld method and different structural and microstructural models. Bond valence and Fourier methods were used to determine bond distances and neutron/electron density maps. LaBaCo2O6−δ exhibits a higher concentration of oxygen vacancies than La0.5Ba0.5CoO3−δ, because the O atom is weakly bonded to the LaO layers. The anisotropic atomic displacement and the neutron density distribution suggest a two‐dimensional O‐migration path for LaBaCo2O6−δ and a three‐dimensional path for La0.5Ba0.5CoO3−δ.The mechanism of electrical conductivity is via electron holes with high mobilities (μLa0.5Ba0.5CoO3−δ = 2.49 cm2 V−1 s−1 and μLaBaCo2O6−δ = 1.48 cm2 V−1 s−1 at room temperature) and low activation energy (EaLaBaCo2O6−δ = 0.019 eV and EaLa0.5Ba0.5CoO3−δ = 0.030 eV). It has also been found that the higher electronic and ionic conductivities in La0.5Ba0.5CoO3−δ compared to those in LaBaCo2O6−δ are due to the higher dimensionality of transport and to greater overlapping between the Co 3d and O 2p orbitals.