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 was examined at by feeding humidified fuel, . 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 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 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 by a focused ion beam scanning electron microscopy technique, whereas that of the as-prepared anode was .