Visualization by Neutron Diffraction of 2D Oxygen Diffusion in the Sr0.7Ho0.3CoO3-δ Cathode for Solid-Oxide Fuel Cells

Sr0.7Ho0.3CoO3-delta oxide has been recently described as an excellent cathode material (1274 mW cm(-2) at 850 degrees C with pure H-2 as fuel(1)) for solid oxide fuel cells (SOFCs) with LSGM as electrolyte. In this work, we describe a detailed study of its crystal structure conducted to find out the correlation between the excellent performance as a cathode and the structural features. The tetragonal crystal structure (e.g., I4/mmm) basically contains layers of octahedrally coordinated Co2O(6) units alternated with layers of ColO(4) tetrahedra sharing corners. An "in situ" neutron power diffraction (NPD) experiment, between 25 and 800 degrees C, reveals the presence of a high oxygen deficiency affecting O4 oxygen atoms, with large displacement factors that suggest a large lability and mobility. Difference Fourier maps allow the visualization at high temperatures of the 2D diffusion pathways within the tetrahedral layers, where O3 and O4 oxygens participate. The measured thermal expansion coefficient is 16.61 x 10(-6) K-1 between 300 and 850 degrees C, exhibiting an excellent chemical compatibility with the electrolyte.