Fuel Electrode Resistance as Initiator for Ni Migration Caused Degradation of Solid Oxide Electrolysis Cells

One major degradation mechanism in Ni-yttria-stabilized-zirconia (Ni/YSZ) fuel electrodes is the migration of Ni away from the fuel electrode-electrolyte interface. This degradation mechanism continues to pose a significant challenge in context of fuel electrode supported cell (FSCs). It significantly impacts both electrochemical performance and electrode lifetime. Ni migration is typically observed when operating at high current densities that lead to high overpotentials. In this work, two fuel electrode supported cells are compared, both with respect to initial electrochemical performance and lifetime. The two cells had similar initial overall resistance when operated in steam electrolysis at −0.75 A cm −2 , inlet of H 2 O/H 2 :90/10 at 750 °C. Cell 1 initially had low resistance due to physical processes i.e. concentration polarization (R conc ) and high resistance due to electrochemical processes at the Ni/YSZ electrode (R Ni/YSZ ); while Cell 2 was designed to have high concentration polarization (R conc ) and low resistance due to electrochemical processes at the Ni/YSZ electrode. This work shows that it is R Ni/YSZ —not R conc or total resistance - that is the determining resistance contribution for fuel electrode degradation and Ni migration. Furthermore, post-test analysis show presence of impurities and a microstructure indicating a pre-cursor state for Ni migration.