Microstructure Alteration Analysis of Ni/YSZ Cermet by Comb-shaped Ni Patterned Electrode

Degradation of solid oxide cells can be partially attributed to the microstructural changes in Ni/YSZ fuel electrodes owing to Ni migration. This study aims to evaluate the microstructural evolution of Ni/YSZ fuel electrodes as a function of the oxygen potential along the thickness direction. To this end, comb-shaped Ni-patterned electrodes were designed on the top layer of a YSZ thin film using two different systems: (a) a symmetrical Ni-patterned electrode and (b) an asymmetrical Ni-Pt electrode with a reference electrode. In the symmetrical electrode, one side of the Ni-patterned electrode operated at the fuel cell (FC) mode, exhibiting expansion that led to an increase in triple-phase boundary (TPB) length and a decrease in electrolyte width. Conversely, the Ni-patterned electrodes that operated in electrolysis (EC) mode showed a slight migration away from the electrolyte. Detailed microstructural changes in the EC mode were examined using the asymmetrical electrode, revealing a correlation between water vapor content and Ni morphology. The results suggest two important points: 1. The amount of water vapor adsorbed on the electrode surface causes the decrease of the Ni wettability due to the decrease of oxygen potential; 2. The microstructure change across the electrode length is affected by the distribution of the oxygen potential.