Abstract
The substitutional doping of Ca2+, Sr2+, and Ba2+ on the Sm-site in the cubic perovskite SmCoO3 is reported to improve both electronic and ionic conductivities for applications as solid oxide fuel cell (SOFC) cathodes. Hence, in this study we have used density functional theory (DFT) calculations to investigate dopant configurations at two different dopant concentrations: 25 and 50%. To preserve the electroneutrality of the system, we have studied two different charge compensation mechanisms: the creation of oxygen vacancies, and electronic holes. After examining the electronic structure, charge density difference, and oxygen vacancy formation energies, we concluded that oxygen vacancy charge compensation is the preferred mechanism to maintain the electroneutrality of the system. Furthermore, we found that the improvement of the electronic conduction is not a direct consequence of the appearance of electron holes, but a result of the distortion of the material, more specifically, the distortion of the Co-O bonds. Finally, molecular dynamics were employed to model ionic conduction and thermal expansion coefficients. It was found that all dopants at both concentrations showed high ionic conduction comparable to experimental results.
Highlights
Solid oxide fuel cells (SOFC) are important potential replacements of traditional power sources, and offer a clean and efficient chemical-to-electrical energy conversion process.[1,2,3] to make these devices more widely available and applicable, their operating temperature and costs have to be lowered
The factor influencing the efficiency of intermediate temperature SOFC (IT-SOFC) cathodes is the catalytic efficiency towards the oxygen reduction reaction, which depends on the surface oxygen reduction and oxygen bulk diffusion
We should use Site-Occupancy Disorder program (SOD) again to determine the non-equivalent positions for the oxygen vacancy in the doped system
Summary
Unlike traditional cathode materials such as La1ÀxSrxMnO3Àd (LSM), which loses efficiency at these low temperatures due to polarization resistance, cobalt-based perovskites have shown better performance and have been suggested as suitable materials for IT-SOFC,[5] as their reported properties include better mixed ionic and electronic conduction, low polarization resistance, and lower overpotentials.[6,7] Their higher ionic conductivity is a consequence of the lower activation energies required for the oxygen to migrate. Experimental studies conducted on Sm1ÀxAxCoO3Àx/2 indicate that they could be promising materials for IT-SOFC cathodes, questions remain why samarium cobaltates show better performance than doped lanthanum manganite.[2] in this paper, we investigate three common SmCoO3 dopants; Ca2+, Sr2+, and Ba2+, at two different dopant concentrations (x); x = 0.25, and 0.5. Using a combination of density functional theory and molecular dynamics simulations, we have investigated two different charge compensation schemes, the electronic and magnetic structure, oxygen diffusion, and the thermal expansion coefficients. Whereas MD is used to study thermal properties and oxygen diffusion at different temperatures
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