Fig. 5: Formation of the high-performance air electrode of BCFN covered with fine BCFN NPs with less Nb.

a. TEM image and elemental (Ba, Co Fe, and Nb) mapping of a BCFN grain after electrochemical testing at 650 °C; b. Elemental profile along the scanning line shown in the TEM image; c. Comparison of computed segregation energies (J m−2) for stoichiometric Ba(B0.5B′0.5)O3 (B,B′ = Co, Fe, or Nb); d. Illustration of CoO-terminated BCFN(001) surface models representing segregation of Nb from the bulk to the surface; e. Computed segregation energy (eV) for three different dopant cations of Ba0.9(Co0.63Fe0.25Nb0.13)O3; and f. A schematic illustration of the formation of Nb-deficient BCFN NPs on the BCFN air electrode.