The layered double perovskite oxides of the type LnBaCo2O5+δ are proposed as a promising material for Solid oxide fuel cell cathodes because of their distinct oxygen-deficient structure with alternate layers of A-O/B-O/A’-O/B-O… type, high oxygen anion diffusion rate, high oxygen vacancy concentration, and surface exchange coefficient. The present work is focused on the study of NdBa1-xSrxCo2O5+δ as SOFC cathodes. The plane wave density functional theory-based calculations with Hubbard correction are performed to study the oxygen vacancy formation characteristics and surface energetics of the material. The bulk oxygen vacancy formation energies (Eov) have been calculated computationally for oxygen vacancy created in all possible planes (BaSr/O, Nd/O, and Co/O), and the surface energies (γ) of the structure with different terminations (BaSr/Co, Nd/Co, Co/BaSr and Co/Nd) along (001) direction. For x=0, 0.25, and 0.50, BaSr/O planes have the highest oxygen vacancy formation energies, showing difficulty in oxygen vacancy creation in the BaSr/O plane as compared to other planes. This suggests less oxygen anion diffusivity in the BaSr/O plane. The Nd/O plane is observed to have the lowest oxygen vacancy formation energy among all the three possible planes in (001) direction of bulk NdBa1-xSrxCo2O5+δ. This shows, Nd/O plane to have high oxygen vacancy concentration. For NdBaCo2O5+δ, low surface energies have been observed for Ba/Co termination. Due to this, the Ba ions have the tendencies to segregate towards the surface. Doping NBCO with Sr has also shown a similar trend in surface energies of BaSr/Co terminal surface and doping one-fourth and half of the Ba with Sr resulted in an improved bulk oxygen vacancy characteristic of the BaSr/O plane.

Role of Sr doping on oxygen vacancy formation characteristics and surface energetics of NdBa1-xSrxCo2O5+δ for SOFC cathodes

ACS Fall 2021

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