Performance Deterioration of Ni-YSZ Anode Induced by Electrochemically Generated Steam in Solid Oxide Fuel Cells

Nickel-yttria-stabilized zirconia (Ni-YSZ) cermet is a conventional anode for use in solid oxide fuel cells, and its composition and microstructure are carefully controlled to achieve high performance and long-term stability. In this study, the performance stability of the electrolyte-supported cell (Ni-YSZ vertical bar YSZ vertical bar LSM) was examined at 1000 degrees C by feeding humidified fuel, x% H(2)O-(100-x)% H(2). The influence of the cermet composition on degradation was also studied. The degradation behavior was significantly dependent on the fuel humidity and cermet composition. In the case of Ni-YSZ with a volume ratio of 50 to 50, peculiar phenomena were observed. When the fuel of 30% H(2)O-70% H(2) was supplied to the anode at the terminal voltage of 0.7 V, the current density decreased gradually soon after the discharge of up to 69 h, followed by a sudden drop in the current density. After the subsequent open-circuit holding, the performance was partially recovered in the discharge operation. This behavior of the degradation-recovery was reversibly repeated upon the discharge-open-circuit holding operation. Under the 40% H(2)O-60% H(2) atmosphere, an irreversible performance deterioration was observed accompanied with a drastic decrease in the volume-specific triple-phase boundary (TPB) length. The TPB length of the degraded anode was evaluated to be 1.66-1.68 mu m mu m(-3) by a focused ion beam scanning electron microscopy technique, whereas that of the as-prepared anode was 2.49 mu m mu m(-3).