Oxygen chemical potential variation in ceria-based solid oxide fuel cells determined by Raman spectroscopy

The profile of oxygen chemical potential in 20 mol% Sm-doped ceria Ce0.8Sm0.2O2−δ (SDC) at 1273 K under the open-circuit conditions of solid oxide fuel cells was determined using Raman spectroscopy. SDC pellets were annealed in various atmospheres, and a peak intensity of a Raman band of SDC in the range 540–600 cm−1, which has been assigned to a band that originates in the oxygen vacancies, increased with decreasing oxygen partial pressure [P(O2)] upon annealing. A clear relationship between the peak area of the oxygen-vacancy band and P(O2) upon annealing was obtained. This relationship was used to determine the profile of oxygen partial pressure, P(O2), in SDC located between fuel and air. The experimental profile was in good agreement with that obtained theoretically. The profile revealed that most part of SDC was mixed conductive and only a thin layer adjacent to the air side remained purely ionic conductive under the open-circuit conditions of SOFCs.