5 mol% TiO2-doped Ni–YSZ anode cermets for solid oxide fuel cells

The influence of doping YSZ (8 mol% yttria stabilized zirconia) with 5 mol% TiO2 on the thermal expansion coefficient, electrical conductivity and microstructure was examined for different cermets as a function of Ni-content. Thermal expansion measurements showed that TiO2 contributes to the reduction of the thermal expansion coefficient values of the cermet material. The incorporation of TiO2 into the YSZ lattice was found to reduce slightly the ionic conductivity of the pure ceramic, while under reducing conditions the electronic contribution, due to the reduction of Ti+4 to Ti+3, results in a decrease of the activation energy for conduction in the order of 13%. For the TiO2-doped cermets the electrical conductivity was always better than that of the undoped, exhibiting a lower degradation rate at 1000°C. Based on microstructure examination of the samples, this degradation was attributed to the lower agglomeration trend of the Ni-particles of the doped cermets compared to the Ni–YSZ cermet.