Ni-YSZ cermets for solid oxide fuel cell anodes via two-step firing

The electrochemical performance and dimensional stability of Ni-YSZ cermets, conventionally used as solid oxide fuel cell anodes, depend strongly on their microstructure and therefore fabrication conditions. This work was focused on the assessment of a less common two-step firing procedure for fabrication of Ni-YSZ cermets with comparatively low nickel fraction of 30 vol.%. The impact of different firing parameters including peak temperature (1623-1723 K), heating/cooling rate (4-10 K/min), and isothermal treatment temperature (1473-1573 K) and time (2-8 h), on the porosity and electrical conductivity of cermets was assessed employing Taguchi experimental planning. The applied procedure yielded Ni-YSZ composites with porosity 26-35% and electrical conductivity ranging from 170 to 420 S/cm at 873-1173 K in 10%H2-N2 atmosphere. Microstructural studies indicated that the conductivity is determined mainly by Ni particle size distribution. Analysis of results suggests that, for the studied range of sintering parameters, a higher peak temperature and ramp rate are favorable for the improvement of conductivity, whereas isothermal dwell temperature and time have a rather minor effect on the conductivity level.