Nickel coarsening in annealed Ni/8YSZ anode substrates for solid oxide fuel cells

In order to study the nickel coarsening in porous Ni/8YSZ anode cermets of solid oxide fuel cells (SOFC), a series of exposure tests was carried out with anode substrates used in SOFC development at the Research Centre Jülich. The changes in electrical conductivity as well as in the microstructure of the material were investigated. The microstructure of the cermets was characterized by digital on-line image analysis and microstructural parameters were determined for the metallic and the ceramic phase as well as for porosity. A decrease of 33% of the initial electrical conductivity was measured after exposing the cermet in Ar/4% H2/3% H2O at 1000°C for 4000 h, which is linked to the agglomeration of the metallic particles of this material. The durability of anode cermets for operations of up to 40 000 h was estimated on the basis of the measured grain coarsening and the decrease of conductivity. The microstructural parameters — like volume fraction, particle and pore size — were used to model the electrical conductivity by theoretical microstructure–property relationships.