The effect of oxygen vacancies on proton conduction in 12.5% Sc-doped BaZrO3
Date
2020-07-06
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Abstract
Fuel cells avoid the combustion process and hence are both more efficient and environmentally friendly than the common practice of burning fuels at power plants. Y-doped barium zirconium oxide (BaZrO3) represents one of the most promising materials for stationary hydrogen fuel cells due to its ability to conduct hydrogen ions (protons)[1, 2]. Recently, it is found that Sc-doped BaZrO3 has exhibited comparable proton conductivity as Y-doped (BaZrO3)[3]. However, the introduction of the less positive dopant defects Sc3+ and Y 3+ at the Zr4+ site, leads to the formation of proton traps. Inspired by studies suggesting that oxygen vacancies decrease trapping near dopant defects, this study aims to understand the effect of an oxygen vacancy on the minimum energy pathways, proton traps, and overall proton conduction in 12.5% Sc doped BaZrO3 Perovskite[4]. Density functional theory (DFT) with the PBE functional in the Vienna ab-initio simulation package (VASP)[5] was used to find the total electronic energy for perovskite configurations. The conjugate-gradient minimization method is used to find the lowest energy structures for doped barium zirconium oxide systems starting from the 23 possible Glazer[6] distortions. The Nudged Elastic Band (NEB) method was used to find activation barriers for oxygen vacancy motion. The influence of a dopant nearest neighbor oxygen vacancy on the proton energy landscape was determined by finding the relative energies for chemically distinct proton binding sites as well as transition states between sites close and far from the oxygen vacancy. Finally, Kinetic Monte Carlo (KMC) simulation is used to find the most abundant limiting barrier and explore the proton conduction trajectory.
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Perovskite, fuel cell