Microstructural characterization of SOFC Ni–YSZ anode composites by low-voltage scanning electron microscopy

Abstract

A lack of contrast between nickel and yttria stabilized zirconia (YSZ) in scanning electron microscopy (SEM) has long been an obstacle for complete microstructural characterization of porous Ni–YSZ anodes for solid oxide fuel cells (SOFC). In this paper a technique to achieve contrast between Ni and YSZ is described. The technique is based on imaging of a non-coated sample surface with an ordinary lateral secondary electron detector at a low voltage in a field emission (FE) SEM. A technique to visualize the degree of percolation of the electrically conducting phase (Ni) by low-voltage SEM is also developed. For this purpose the FE–SEM and an inlens secondary detector is utilized and applied to the same type of samples as above. A combination of these two techniques offers the possibility to fully characterize the microstructure of the Ni–YSZ anode, providing parameters such as size and distribution of all four components (percolating Ni, non-percolating Ni, YSZ and pores).