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 PrBaCo2O5+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.