The orthorhombic phase of FeNbO4, a promising anode material for solid oxide fuel cells (SOFCs), exhibits good catalytic activity toward hydrogen oxidation. However, the low electronic conductivity of the material specifically in the pure structure without defects or dopants limits its practical applications as an SOFC anode. In this study, we have employed density functional theory (DFT + U) calculations to explore the bulk and electronic properties of two types of doped structures, Fe0.9375A0.0625NbO4 and FeNb0.9375B0.0625O4 (A, B = Ti, V, Cr, Mn, Co, Ni) and the oxygen-deficient structures Fe0.9375A0.0625NbO3.9375 and FeNb0.9375B0.0625O3.9375, where the dopant is positioned in the first nearest neighbor site to the oxygen vacancy. Our DFT simulations have revealed that doping in the Fe sites is energetically favorable compared to doping in the Nb site, resulting in significant volume expansion. The doping process generally requires less energy when the O-vacancy is surrounded by one Fe and two Nb ions. The simulated projected density of states of the oxygen-deficient structures indicates that doping in the Fe site, particularly with Ti and V, considerably narrows the bandgap to ∼0.5 eV, whereas doping with Co at the Nb sites generates acceptor levels close to 0 eV. Both doping schemes, therefore, enhance electron conduction during SOFC operation.

中文翻译：

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用于固体氧化物燃料电池应用的斜方 FeNbO4 材料中的阳离子掺杂和氧空位：密度泛函理论研究

FeNbO4 的斜方相是一种有前景的固体氧化物燃料电池（SOFC）阳极材料，对氢气氧化表现出良好的催化活性。然而，该材料的低电子电导率，特别是在没有缺陷或掺杂剂的纯结构中，限制了其作为 SOFC 阳极的实际应用。在本研究中，我们采用密度泛函理论 (DFT + U) 计算来探索两种类型的掺杂结构 Fe0.9375A0.0625NbO4 和 FeNb0.9375B0.0625O4 (A, B = Ti, V, Cr、Mn、Co、Ni）和缺氧结构 Fe0.9375A0.0625NbO3.9375 和 FeNb0.9375B0.0625O3.9375，其中掺杂剂位于距离氧空位最近的第一相邻位置。我们的 DFT 模拟表明，与 Nb 位点掺杂相比，Fe 位点掺杂在能量上更有利，从而导致显着的体积膨胀。当 O 空位被一个 Fe 和两个 Nb 离子包围时，掺杂过程通常需要较少的能量。模拟的缺氧结构的预计态密度表明，Fe 位点的掺杂，特别是 Ti 和 V 的掺杂，将带隙显着缩小至~0.5 eV，而 Nb 位点的 Co 掺杂产生接近 0 eV 的受主能级。因此，两种掺杂方案都增强了 SOFC 运行期间的电子传导。