Surface Cation Segregation and Chromium Deposition on the Double-Perovskite Oxide PrBaCo₂O_5+δ

The surface chemistry and the Cr tolerance ability of oxygen electrodes play a vital role in the performance and long-term stability of solid oxide cells (SOCs). In this paper, the surface cation segregations on the double-perovskite oxide PrBaCo₂O_5+δ (PBCO) and its relationship with Cr deposition are reported. During high-temperature annealing in an O₂ atmosphere, the elements Ba and Co diffuse out of the lattice and form many BaO and Co₃O₄ precipitates on the surface, mainly located at grain boundaries. In the presence of volatile Cr species, the observation of BaCrO₄, but not CoCr₂O₄, on a segregated PBCO surface reveals that the Cr deposition preferentially takes place on segregated BaO rather than on Co₃O₄ precipitates. Our results show that segregated BaO precipitates are very active toward Cr vapor and PBCO is not a Cr-tolerant oxygen electrode for SOCs operating at high temperatures, despite its superior electrochemical performance.