3D Microstructural Characterization of Ni/YSZ Electrodes Exposed to 1 Year of Electrolysis Testing

10 Long-term operation strongly affects the microstructure of Ni/YSZ cermets used in state of the art fuel 11 electrodes for solid oxide cells. The microstructural changes are considered to heavily affect the cell 12 degradation. In this paper, the characterization of the Ni/YSZ electrode of a solid oxide electrolysis cell tested 13 as part of a stack tested for 1 year was performed through focused ion beam-scanning electron microscopy and 14 energy dispersive X-ray spectroscopy. A reference cell and two locations of interest in the tested cell were 15 selected: one at the steam inlet side and the other at the outlet. Considerable microstructural changes were 16 observed in the tested cell compared to the reference cell and between the inlet and outlet side. A decrease in 17 Ni (from 30 % in the reference cell to 24 % in the tested cell), and in percolating triple phase boundaries length 18 (from 2.83 μm/μm in the reference cell to 0.76 μm/μm in the tested cell) was observed in the active fuel 19 electrode. Based on the results of this work and previous studies we hypothesize that the degradation trend 20 between different operating conditions at the inlet and outlet of the cell is related to the current redistribution 21 inside the cell. 22