Effect of Ni content in SOFC Ni-YSZ cermets: A three-dimensional study by FIB-SEM tomography

SOFC anodic cermets with varying Ni concentrations have been studied in terms of electric percolation and electrochemical activity. Serial sectioning using focused ion beam-scanning electron microscopy (FIB-SEM) has been implemented to reconstruct the three-dimensional microstructure. A Passive Voltage Contrast technique has also been used to evaluate the degree of percolation of the electrically conducting phase (Ni) in the Ni-YSZ cermets. Volumetric ratios, connectivity of the phases and effective electrical conductivity have been estimated to establish a relation between the volumetric ratio of Ni and the electrical conductivity. These results were then correlated with experimental measurements. From the 3D reconstructions, interface features (interface and surface areas, three-phase boundary length: TPBL) and ionic effective conductivities have been compared, enabling a characterization of the electrochemical activity of the samples. After reduction of the initial NiO, 40:60 vol.% Ni:YSZ appeared to be the optimal composition, providing an anode with high electronic conductivity and the largest active TPBL.

► Electric percolation and electrochemical activity of SOFC anodic cermets with various Ni concentrations. ► 3D images of about 1000 μm3 volumes from FIB tomography. ► Calculation of volume fractions, volumetric connectivity of the individual phases, specific surface and interface areas and three-phase boundary length. ► 3D finite difference method evaluation of effective thermal, electronic and ionic conductivities as well as of the tortuosity of the solid phases.