Density functional theory investigation of the electronic structure and defect chemistry of Sr 1-x K x FeO 3
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unctional Oxides Research Letter
Density functional theory investigation of the electronic structure and defect chemistry of Sr1−xKxFeO3 Andrew M. Ritzmann, Department of Chemical and Biological Engineering, Princeton University, Princeton, NJ 08540, USA† Johannes M. Dieterich, Department of Mechanical and Aerospace Engineering, Princeton University, Princeton, NJ 08540, USA Emily A. Carter, Department of Mechanical and Aerospace Engineering, Program in Applied and Computational Mathematics, Andlinger Center for Energy and the Environment, Princeton University, Princeton, NJ 08540, USA Address all correspondence to Emily A. Carter at [email protected] (Received 26 May 2016; accepted 18 July 2016)
Abstract Solid oxide fuel cells (SOFCs) efficiently generate electricity, but high operating temperatures (Top > 800 °C) limit their utility. Reducing Top requires mixed ion–electron conducting (MIEC) cathode materials. Density functional theory is used here to investigate the role of potassium substitutions in the MIEC material Sr1−x Kx FeO3 (SKFO). We predict that such substitutions are endothermic. SrFeO3 and SKFO have nearly identical metallic electronic structures. Oxygen vacancy formation energies decrease by ∼0.2 eV when xK increases from 0 to 0.0625. SKFO is a promising SOFC MIEC cathode material; however, further experimental investigations must assess its long-term stability at the desired operating temperatures.
Solid oxide fuel cells (SOFCs) provide a clean and efficient means of generating electrical power from various fuel sources.[1] However, high operating temperatures (Top > 800 °C) reduce the overpotential arising from standard La1−xSrxMnO3 cathodes, but increase material costs and shorten cell lifetimes.[2] Intermediate-temperature (600 °C < Top < 800 °C) SOFCs have potential to overcome these deficiencies but in turn require alternative, mixed ion–electron conducting (MIEC) cathode materials to increase the active region and reduce the cathode overpotential.[3] Useful MIEC cathode materials must allow for facile electronic and ionic conductivity. La1−xSrxCo1−yFeyO3 remains the reference MIEC cathode[4–7] although many other cathode materials show promising electrochemical behavior. These include Ba1−xSrxCo1−y FeyO3 (BSCF), Sr2Fe2−xMoxO6 (SFMO), and Sr1−xKxFeO3 (SKFO).[8–10] Many experimental studies have illuminated the structural properties, oxygen transport kinetics, and electrochemical performance of LSCF, BSCF, and SFMO.[6,10–13] Far less is known about SFKO. Hou et al. reported that cathodes of Sr0.9K0.1FeO3 (with a La0.8Sr0.2Ga0.83Mg0.17O3−δ, or LSGM, electrolyte and a Sr2MgMoO6 anode) produced a current density competitive with LSCF at 800 °C.[9] Repetitive cycling of the cell between open circuit voltage and 0.4 V caused no loss in the observed power density.[9] Furthermore, SFKO cathodes contain no Co, which improves their cost-effectiveness.[14]
A previous error in this article’s header has been corrected. † Permanent address: The Pennington School, 112 W. Delaware Avenue, Pennington, NJ 08534,
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