Microstructure Evolution Analysis of Ni/YSZ Cermet Electrode Using Cross-Sectional Model Cells

Abstract 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 that the amount of water vapor adsorbed on the electrode surface causes the decrease of oxygen potential at TPB. This causes the decrease in the wettability that led to significant change of Ni microstructure across the electrode length.