Abstract
LaFeO3, a mixed ionic electronic conductor, is a promising cathode material for intermediate temperature solid oxide fuel cells (IT-SOFC). Key to understanding the electronic and ion conducting properties is the role of defects. In this study ab initio and static lattice methods have been employed to calculate formation energies of the full range of intrinsic defects—vacancies, interstitials, and antisite defects—under oxygen rich and oxygen poor conditions, to establish which, if any, are likely to occur and the effect these will have on the properties of the material. Under oxygen rich conditions, we find that the defect chemistry favors p-type conductivity, in excellent agreement with experiment, but contrary to previous studies, we find that cation vacancies play a crucial role. In oxygen poor conditions O2– vacancies dominate, leading to n-type conductivity. Finally, static lattice methods and density functional theory were used to calculate activation energies of oxide ion migration through this material. Three pathways were investigated between the two inequivalent oxygen sites, O1 and O2; O2–O2, O1–O2, and O1–O1, with O2–O2 giving the lowest activation energy of 0.58 eV, agreeing well with experimental results and previous computational studies.
Highlights
With the issues of environmental impact and security surrounding energy generation, the need for a clean and renewable alternative is becoming increasingly essential
Solid oxide fuel cells (SOFCs) offer many advantages over these as they are the cleanest and most efficient:[3] they alleviate the need for corrosive liquids and have been shown to be reliable when operated continuously.[1]
The formation energies of intrinsic defects, both neutral and charged, within the two chemical potential environments, have been calculated using the density functional theory (DFT) technique
Summary
With the issues of environmental impact and security surrounding energy generation, the need for a clean and renewable alternative is becoming increasingly essential. Different types of fuel cells have been investigated, including polymer electrolyte membrane[1] and proton exchange membrane fuel cells.[2] solid oxide fuel cells (SOFCs) offer many advantages over these as they are the cleanest and most efficient:[3] they alleviate the need for corrosive liquids and have been shown to be reliable when operated continuously.[1] The efficiency of these fuel cells depends on their component materials, finding optimal materials is an active field of research. Fuel cells have three main components: the cathode, electrolyte, and anode. Typically air, is reduced at the cathode producing O2− ions which migrate across the electrolyte to the anode where they react with a fuel, usually hydrogen. Research into SOFCs has focused on reducing the temperature of operation to between 500 and 800 °C
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