  Solid oxide fuel/electrolyzer cell (SOFC/SOEC) converts energy between
chemical and electrical forms inversely. Yet electrolyte degradation takes
place much more severe for SOEC than SOFC during long-term operations. By
solving transport equations, we found very large oxygen potential gradients and
sharp oxygen potential transitions at grain boundaries of polycrystalline
SOFC/SOEC electrolyte. Surprisingly, an inversion of oxygen potential
transitions was identified, suggesting a fundamentally different transport
mechanism for minor electronic charge carriers. Such findings could be critical
to understand and eliminate SOFC/SOEC degradations in practical applications.
