Sinterability, microstructures and electrical properties of Ni/Gd-doped ceria cermets used as anode materials for SOFCs

The influence of Ni content in Ni–CGO cermets on their electrical conductivity was investigated in order to create the most suitable microstructure. Ni–CGO (50/50, 45/55 and 40/60 wt%) powder mixtures were prepared by the polymeric organic complex solution method using ethyleneglycol as a polymerized soluble alcohol in water. By heat treatment a composite of ultrafine nickel oxide homogeneously dispersed in the CGO ceramic matrix was attained. After sintering of NiO–CGO composites in air at 1350 °C for several times and reducing treatment in N2 90%–H2 10% atmosphere, the microstructures showed a uniform distribution of porous metallic Ni particles surrounded by microporous spaces with total porosity (closed and opened) of ≈20–25%. The electrical properties of Ni–CGO cermets sintered at 1350 °C for 2 h were studied using impedance spectroscopy in the temperature range from 500 to about 700 °C in argon atmosphere. The Ni–CGO cermets showed metallic behaviour over all the range at temperatures studied, indicating a uniform and fine-grained microstructure in which the Ni–Ni particle contacts were predominant.