Jin Zongzi, Peng Ranran, Xia Yunpeng, Wang Zhenbin, Liu Wei
CAS Key Laboratory of Materials for Energy Conversion, Department of Materials Science and Engineering, University of Science and Technology of China Hefei 230026 P. R. China
Department of Physics, Technical University of Denmark 2800 Kongens Lyngby Denmark.
RSC Adv. 2020 Nov 2;10(66):39988-39994. doi: 10.1039/d0ra08097g.
Understanding the electrode properties at the atomistic level is of great benefit to the evaluation of electrode performance and design of better electrode materials in solid oxide fuel cells. In this work, density functional theory (DFT) calculations are employed to investigate the formation and conducting behaviors of oxygen vacancies and proton defects in Ruddlesden-Popper oxide SrEuFeO (SEFO), which has been experimentally characterized as a promising cathode. The calculation results suggest both oxygen vacancies and proton defects can be formed in SEFO, and especially, the formation of these defects is largely dependent on oxygen sites in the special crystal structure with alternative stacking of rock-salt layers and double-layered perovskite slabs. The oxygen vacancies within the perovskite slabs have very low formation energies, but demonstrate high energy barriers for migration and low hydration properties; while in the case of those in the rock salt layers, it's contrary. Interestingly, protons have similar migration abilities in the perovskite slabs and rock salt layers. And therefore, increasing the vacancy concentration of the rock salt layer is beneficial to increase the concentration of proton defects and to improve the proton conductivity. DFT calculations also indicate that substituting Zn for Fe in SEFO can largely depress the oxygen vacancy formation energy, which helps to increase the concentration of both defects. Importantly, the energy barriers for migration of both oxygen ions and protons are barely enhanced, implying a negligible trapping effect of the Zn dopant.
在原子层面理解电极特性对于评估固体氧化物燃料电池的电极性能以及设计更优的电极材料大有裨益。在本工作中，采用密度泛函理论（DFT）计算来研究Ruddlesden-Popper氧化物SrEuFeO（SEFO）中氧空位和质子缺陷的形成及传导行为，SEFO已通过实验表征为一种有前景的阴极材料。计算结果表明，SEFO中既能形成氧空位也能形成质子缺陷，特别地，这些缺陷的形成很大程度上取决于具有岩盐层和双层钙钛矿板交替堆叠的特殊晶体结构中的氧位点。钙钛矿板内的氧空位形成能非常低，但迁移能垒高且水合性能低；而岩盐层中的氧空位情况则相反。有趣的是，质子在钙钛矿板和岩盐层中的迁移能力相似。因此，增加岩盐层的空位浓度有利于提高质子缺陷浓度并改善质子传导率。DFT计算还表明，在SEFO中用Zn替代Fe可大幅降低氧空位形成能，这有助于增加两种缺陷的浓度。重要的是，氧离子和质子迁移的能垒几乎没有增加，这意味着Zn掺杂剂的俘获效应可忽略不计。
