Highlights on the Anisotropic Oxygen Transport Properties of Nickelates with K2NiF4-Type Structure: Links with the Electrochemical Properties of the Corresponding IT-SOFC’s Cathodes

Abstract

Understanding fundamental aspects of oxygen self-diffusion in MIEC materials is crucial for the discovery of next-generation of cathode materials. Perovskite-type oxides are the most studied material, the oxide ion diffusion being based on the vacancy migration in a cubic-like disordered network. According to results of predictive atomistic simulations, a current trend concerns experimental works related to perovskite-derived phases with anisotropic structures where oxide ion transport is no longer based on oxygen vacancies but on oxygen interstitials. Then a particular attention is here paid to the nickelates Ln2NiO4+δ, Ln=La, Nd, Pr, with the orthorhombic K2NiF4-type structure characterized by a high c/a lattice parameters ratio. We have completed our previous work performed on single crystals and thin films aiming at experimentally determining the oxygen diffusion and surface exchange coefficients using the so-called IEDP method, as a function of the crystallographic orientation as well as the rare-earth cation. Highly anisotropic oxygen diffusion properties have been evidenced and the activation energies have been compared. Moreover, the electrochemical performances (polarization resistance measurements) of the corresponding porous cathode materials were previously determined in the literature in the same T-range, using symmetrical half cells including YSZ as electrolyte. The results are discussed with regards to the oxygen diffusion properties of the electrodes.