Study on local morphological changes of nickel in solid oxide fuel cell anode using porous Ni pellet electrode

Morphological change of nickel, especially the aggregation of nickel, in solid oxide fuel cell anode is an important deactivation mechanism which results in long-period degradation of anode. In order to study the mechanisms which cause local morphological changes of nickel in solid oxide fuel cell anode, porous nickel pellet, which is mechanically pressed against dense YSZ pellet with LSM cathode, was employed as the anode of the cell. The cell was tested by static-potential method in hydrogen with different humidities environment for 60 h. The study focused on the vicinity of three phase boundary which concentrated at nickel–YSZ interface. After the discharging test, the cell performance and the microstructure at nickel–YSZ contacting point of interface were studied and correlated to nickel morphological changes. The interlocking effect and the spreading of densified nickel layer phenomena were observed between nickel and YSZ substrate after discharging with an anode to cathode terminal voltage of 0.6 V. Humidity enhanced nickel surface diffusion and humidity gradient driving vaporization–deposition mechanism, which caused the growing and merging of independent nickel droplets, were used to explain the local morphological changes and redistribution of nickel inside and along the edge of YSZ surface bonded nickel cluster, respectively. The bulk nickel morphological changes were also studied to support the humidity enhanced nickel surface diffusion mechanism. The competition of interlocking effect, nickel redistribution at TPB and bulk nickel sintering finally determined the cell performance.