Abstract Doped CeO2 is a very promising electrolyte for intermediate temperature solid oxide fuel cells (IT-SOFCs). To further improve the performance of the CeO2-based electrolyte, co-doping two different elements into CeO2 is a feasible method, however the co-doping effect on the ionic conductivity is not well understood and whether it is synergistic or average is even controversial. In order to gain a fundamental understanding of the co-doping effect, the microscopic properties of co-doped CeO2 are calculated using the DFT+U method. Density of states, band structures, oxygen vacancy formation energies, defect association energies, and oxygen vacancy migration energies are systematically calculated for In3+, Sm3+ single-doped and co-doped CeO2. Based on our calculations, we find that the coexistence of the two doped ions in the local structures of the doped CeO2 can suppress the reduction of Ce4+ to Ce3+, which is beneficial for the decrease of the internal short circuit current of the CeO2-based electrolyte. For In3+ and Sm3+ co-doped CeO2, when the distance between the two doped ions is the first nearest neighbor, the co-doping effect is average. However, when the distance between the two doped ions extends to the second nearest neighbor, the availability of the free oxygen vacancies is synergistically enhanced. Therefore whether the co-doping effect on the ionic conductivity is average or synergistic is highly dependent on the local structures of the co-doped CeO2 which are difficult to control in experiments, offering a reasonable explanation for controversial experimental results. Our work provides a new atomistic level insight into the co-doping effect in CeO2 which would be helpful for high performance electrolyte development.

中文翻译：

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解开共掺杂对 CeO2 基电解质离子电导率的影响

摘要 掺杂 CeO2 是一种非常有前途的中温固体氧化物燃料电池 (IT-SOFCs) 电解质。为了进一步提高CeO2基电解质的性能，将两种不同的元素共掺杂到CeO2中是一种可行的方法，但共掺杂对离子电导率的影响尚不清楚，是协同还是平均甚至存在争议。为了对共掺杂效应有一个基本的了解，使用 DFT+U 方法计算了共掺杂 CeO2 的微观特性。系统计算了 In3+、Sm3+ 单掺杂和共掺杂 CeO2 的态密度、能带结构、氧空位形成能、缺陷缔合能和氧空位迁移能。根据我们的计算，我们发现掺杂CeO2局部结构中两种掺杂离子的共存可以抑制Ce4+向Ce3+的还原，有利于降低CeO2基电解液的内部短路电流。对于 In3+ 和 Sm3+ 共掺杂的 CeO2，当两个掺杂离子之间的距离为第一近邻时，共掺杂效果是平均的。然而，当两个掺杂离子之间的距离延伸到第二近邻时，自由氧空位的可用性协同增强。因此，共掺杂对离子电导率的影响是平均的还是协同的，高度依赖于实验中难以控制的共掺杂 CeO2 的局部结构，为有争议的实验结果提供了合理的解释。