Comparative Study on Performance Stability of Ni-Oxide Cermet Anodes under Humidified Atmospheres in Solid Oxide Fuel Cells

摘要

The influence of the oxide component in Ni-oxide based cermet anodes on the performance stability was examined at 1000°C with a supply of highly humidified hydrogen, 40% H_2O-60% H_2. Three types of anodes were applied; Ni-samaria-doped ceria (Ni-SDC), Ni-yttria-stabilized zirconia (Ni-YSZ), and Ni-scandia-stabilized zirconia (Ni-ScSZ). Abrupt deterioration in performance was confirmed during constant current operation for the cells with Ni-YSZ and Ni-ScSZ anodes, accompanied with a drastic increase in ohmic resistance between the anode and reference electrode. In contrast, the performance of cell with Ni-SDC anode was pretty stable for 48 h. These differences in performance stability were significantly related to the local partial pressure of steam in the vicinity of the electrochemically active sites because the surface oxidation of nickel particles resulted in the deterioration. The microstructural changes in Ni-YSZ and Ni-SDC anodes upon discharge were also quantified by the dual-beam focused ion beam-scanning electron microscopy (FIB-SEM). The electrochemical behavior observed in each anode had a strong correlation with the anode microstructure such as triple phase boundary length and nickel particle size.