Deposition, Agglomeration and Vaporization of Chromium Oxide by Cathode Polarization Change in SOFC Cathodes

The mechanism of Cr deposition was investigated using NiO/YSZ or NiO/GDC composite cathodes, controlling cathode polarization, and observing the change in Cr distribution. By applying cathode polarization at 200 mV, Cr deposited on the surface of the electrolyte (YSZ or GDC) near the electrode reaction site similarly to the case of typical LSM cathodes. In these cathodes consisting of NiO, the Cr deposition occurred only on the electrolyte surface. After removing the polarization, the deposited Cr partially detached from the electrolyte surface and agglomerated as crystalline Cr2O3 at the interface between NiO and the electrolyte. The deposited Cr may decrease over time by continuous vaporization, and may be agglomerated to form crystalline Cr2O3 transiently. The disappearance of Cr was faster for the NiO/GDC cathode than for the NiO/YSZ cathode. By applying reverse polarization at −200 mV for 1 h, the deposited Cr disappeared from the electrolyte surface for both cathodes. Therefore, the deposition of Cr on the electrolyte seems to be a reversible reaction.