Evaluation of Porous Ni-YSZ Cermets With Ni Content of 0–30 Vol. % as Insulating Substrates for Segmented-in-Series Tubular Solid Oxide Fuel Cells

Nickel was added to a substrate composed of porous Y2O3-stabilized ZrO2 (YSZ) in order to minimize anode damage during redox cycling in segmented-in-series tubular solid oxide fuel cells (SOFCs) with YSZ electrolytes. In this study, the electrical insulating and thermal properties of these materials were evaluated for their suitability as substrates in the tubular SOFCs. When the Ni content was ≤20 vol. %, the porous cermets showed an electrical resistance of ≤67 Ω cm at 900 °C, indicating that the theoretical open circuit voltage for the tubular SOFCs could be achieved. However, the cermet with 20 vol. % Ni was destroyed during the first heating cycle in air because of large isothermal expansion. However, no obvious cracks were observed for cermets with ≤10 vol. % Ni. From the viewpoint of thermogravimetric measurement, this suggests that there are two redox mechanisms for Ni particles in the substrate. They were reduced/oxidized by both the gases and the oxide-ions passing through the YSZ framework. Based on the insulating and thermal properties of the substrate, the optimal composition was found to be approximately 10 vol. % Ni.