Formation and migration of oxygen vacancies in (La,Ba,Sr)(Co,Fe)O3-δ perovskites

E. Kotomin, Yu. A. Mastrikov*, M. M. Kuklja**, R. Merkle

* Institute for Solid State Physics, University of Latvia, Riga ** Materials Science and Engineering, University of Maryland, USA

Mixed conducting (La,Ba,Sr)(Co,Fe)O3-δ perovskites are used as cathode materials in solid oxide fuel cells. Ionic conductivity is not only important for the transport of O through the electrode material, but also decisive for fast kinetics of the oxygen incorporation surface reaction. Thus the reasons for the significantly lower oxygen migration barriers in (Ba,Sr)(Co,Fe)O3-δ compared to (La,Sr)(Co,Fe)O3-δ were investigated by DFT calculations. For (Ba,Sr)(Co,Fe)O3-δ, not only geometrical constraints affect the barrier, but also the O vacancy formation energy (Fig. 1(a)) - i.e. the energy of a redox reaction. This can be understood when the transition state is analyzed in detail: at the saddle point the migrating oxygen O* transfers electron density to the neighboring transition metal cation (decreasing the size of O* and thus the migration barrier), and this electron transfer is easier for perovskites in which also the vacancy formation energy is lower (Fig. 1b).

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E. A. Kotomin, R. Merkle, Y. A. Mastrikov, M. M. Kuklja, and J. Maier: Energy Conversion—Solid Oxide Fuel Cells: First-Principles Modeling of Elementary Processes In Computational Approaches to Energy Materials, A. Walsh, A. A. Sokol, and C. R. A. Catlow, eds., John Wiley & Sons, May 2013.

M. M. Kuklja, E. A. Kotomin, R. Merkle, Yu. A. Mastrikov, and J. Maier: Combined theoretical and experimental analysis of processes determining cathode performance in solid oxide fuel cells Physical Chemistry Chemical Physics 15(15), 5443–5471 (2013). DOI: 10.1039/C3CP44363A

Y. A. Mastrikov, R. Merkle, E. A. Kotomin, M. M. Kuklja, and J. Maier: Formation and migration of oxygen vacancies in La1-xSrxCo1-yFeyO3-δ perovskites: insight from ab initio calculations and comparison with Ba1-xSrxCo1-yFeyO3-δ Physical Chemistry Chemical Physics 15(3), 911–918 (2013). DOI: 10.1039/C2CP43557H

R. Merkle, Yu. A. Mastrikov, E. A. Kotomin, M. M. Kuklja, and J. Maier: First Principles Calculations of Oxygen Vacancy Formation and Migration in Ba1-xSrxCo1-yFeyO3-δ Perovskites Journal of The Electrochemical Society 159(2), B219–B226 (2012). DOI: 10.1149/2.077202jes

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