High Temperature Ni-Diffusion Plaguing Ionic Conductivity of Solid Oxide Cell.

At the operating temperature (∼750°C) of solid oxide cells (SOCs), Ni diffusion has been revealed to cause aging degradations on catalytic performance, electronic conductivity, and mechanical failures. This work discloses that Ni diffusion during the high-temperature (∼1400°C) SOC fabrication process can severely decrease the oxide ion conductivity due to Ni segregation (up to ∼7 at.%) at the YSZ (yttria-stabilized zirconia) grain boundaries (GBs). Combining electrochemical tests and advanced electron microscopy, we reveal that higher Ni enrichment leads to thicker space charge layer and higher space charge potential, which generates a significant GB blocking effect for oxide ion diffusion. We have quantitatively estimated the ionic conductivity drop induced by Ni segregation at the operation temperature range. Utilizing the ultrafast high-temperature sintering technique, we successfully mitigate Ni segregation at GBs, which can double the ionic conductivity at 700°C. This work not only clarifies that Ni segregation at YSZ GBs can significantly plague the ionic conductivity but also demonstrates that mitigating Ni segregation at YSZ GBs is a new avenue to reduce the cell's ohmic resistance and boost the SOC performance.