Abstract
Doped LaMnO3 and SmCoO3 are important solid oxide fuel cell cathode materials. The main difference between these two perovskites is that SmCoO3 has proven to be a more efficient cathode material than LaMnO3 at lower temperatures. In order to explain the difference in efficiency, we need to gain insight into the materials' properties at the atomic level. However, while LaMnO3 has been widely studied, ab initio studies on SmCoO3 are rare. Hence, in this paper, we perform a comparative DFT + U study of the structural, electronic, and magnetic properties of these two perovskites. To that end, we first determined a suitable Hubbard parameter for the Co d-electrons to obtain a proper description of SmCoO3 that fully agrees with the available experimental data. We next evaluated the impact of oxygen and cation vacancies on the geometry, electronic, and magnetic properties. Oxygen vacancies strongly alter the electronic and magnetic structures of SmCoO3, but barely affect LaMnO3. However, due to their high formation energy, their concentrations in the material are very low and need to be induced by doping. Studying the cation vacancy concentration showed that the formation of cation vacancies is less energetically favorable than oxygen vacancies and would thus not markedly influence the performance of the cathode.
Highlights
Solid oxide fuel cells (SOFCs) represent an effective and low-emission alternative to traditional power sources.1–8 Generally speaking, SOFC is composed of three different components: the anode, electrolyte, and cathode
When we examine the calculated chemical potential phase diagrams, it can be seen that SmCoO3 is unstable under oxygen-rich conditions, which favor the formation of CoO2
The projected density of states (PDOSs) of LaMnO3 shows a half-metallic ferromagnetic structure with a β band gap of 1.58 eV calculated from the Fermi level, and a βCBMβVBM band gap of 3.38 eV (Figure 3(a))
Summary
Solid oxide fuel cells (SOFCs) represent an effective and low-emission alternative to traditional power sources. Generally speaking, SOFC is composed of three different components: the anode, electrolyte, and cathode. SOFC is composed of three different components: the anode, electrolyte, and cathode. It is known that the highest catalytic activity is at the triple phase boundary (TPB) where the gas phase, cathode, and electrolyte meet.. At TPB, O2 gas is reduced by the cathode, obtaining O2−, which is driven towards the anode through the electrolyte. LSM degrades at high temperatures owing to a number of reasons: (i) the thermal stress at the grain boundaries with the electrolyte, leading to crack generation; (ii) the consequent delamination of the electrode from the electrolyte, owing to the thermal stress and oxygen bubbling; and (iii) migration of the dopants and impurities to grain boundaries and dislocations, which reduces the effectiveness of the material.. LSM degrades at high temperatures owing to a number of reasons: (i) the thermal stress at the grain boundaries with the electrolyte, leading to crack generation; (ii) the consequent delamination of the electrode from the electrolyte, owing to the thermal stress and oxygen bubbling; and (iii) migration of the dopants and impurities to grain boundaries and dislocations, which reduces the effectiveness of the material. it seems logical that one way to avoid these problems is to reduce the operating temperature, but LSM has been shown to be less efficient under these conditions, with decreased ionic and electronic conductivity.
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