Abstract
Perovskite-type barium-strontium-cobalt-ferrite (BSCF) is a potentially significant material in the development of electrodes for solid oxide fuel cells and electrolysis cells, primarily because of its large oxygen vacancy concentration and mobility. Using density functional theory (DFT) with the DFT + U approach, we perform first principles calculations of oxygen vacancy formation in bulk BSCF with the composition Ba0.5Sr0.5Co0.75Fe0.25O3−δ, in which a range of oxygen deficiencies (0.125 ≤ δ ≤ 0.875) is investigated. Contrary to previous DFT studies for δ = 0.125, DFT + U predicts that the non-stoichiometric structure is more stable than its stoichiometric counterpart with δ = 0, and that this originates from a significantly different atomic and electronic structure following the introduction of the Hubbard U term in the calculations. As more vacancies are created there is no tendency for ordering and the total vacancy formation energy becomes positive and increases as the oxygen deficiency increases. Using ab initio thermodynamics, the heat of formation of BSCF as a function of oxygen partial pressure and temperature is determined and the results are in broad agreement with available stoichiometry measurements.
Highlights
Solid-oxide fuel cells (SOFCs) are electrochemical devices that convert chemical energy into electrical energy, and offer significant prospects for efficient utilization of various fuels with low emissions
The calculated vacancy formation energy is quite different: without adding the O2 energy correction,[22,25] values of 21.34 eV and 21.16 eV are obtained in the O-rich limit using the density functional theory (DFT) + U method for the formation of Co–VO–Co and Co–VO–Fe vacancies respectively, which is in sharp contrast to the standard DFT values of around 0.8–0.9 eV, obtained in the O-rich limit
We found that the vacancy formation energy calculated with the HSE functional (21.19 eV for Co–VO–Co and 21.03 eV for Co–VO–Fe in the O-rich limit) is in good agreement with the DFT + U results
Summary
Solid-oxide fuel cells (SOFCs) are electrochemical devices that convert chemical energy into electrical energy, and offer significant prospects for efficient utilization of various fuels with low emissions. Barium-strontium-cobalt-ferrite (BSCF), which has a perovskite-type structure, has been shown to be a promising cathode material for reduced temperature SOFC operation due to its large concentration of oxygen vacancies, high oxygen ion mobility and significant electrocatalytic activity for the oxygen reduction reaction.[1,2] More recently, it has been shown that BSCF could be a potential candidate as an anode material for solid-state electrolysis cells (SOECs), which perform the reverse electrochemical process to SOFCs.[3]. Much effort has been made towards understanding BSCF with a particular emphasis on the composition Ba0.5Sr0.5Co0.8Fe0.2O32d It has been shown experimentally[4] that the ferrite can exhibit significant oxygen deficiency (d = 0.66–0.81) between 873 and 1173 K and oxygen partial
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
