Abstract The key obstacle preventing the widespread use of chemical looping hydrogen production is the scarcity of high-performance oxygen carrier (OC) materials. Here, for the first time we investigated improved reactivity of all the alkali-doped Fe 2 O 3 OCs by means of density functional theory (DFT) calculations. Firstly, the location of alkali dopants (Li, Na, K, Rb and Cs) in the Fe 2 O 3 crystal structure was studied. Our calculation results showed that all the alkali dopants prefer to be located at the surface of Fe 2 O 3 rather than in the bulk. Then oxygen vacancy formation energies ( E vac ) of Fe 2 O 3 and alkali-doped Fe 2 O 3 OCs, which could be used to evaluate the activity of OC surface oxygen, were calculated via DFT. It was found that the E vac of surface oxygen adjacent to the dopants for all the alkali-doped Fe 2 O 3 are much lower than that for undoped Fe 2 O 3 . The smaller the ionic radius is and the stronger the electronegativity is, the lower the E vac of surface oxygen away from the dopants is. The surface oxygen adjacent to the dopants will show the better activity compared to the one away from the dopants. Finally, we analyzed the effect of alkali dopants on the reactivity of Fe 2 O 3 OC. We concluded that the addition of Li, Na and K dopants are certainly able to enhance the activity of surface oxygen, thereby improving the reactivity of Fe 2 O 3 OC. Compared with Li, Na and K, Rb and Cs will have a worse synergetic effect on the reactivity of Fe 2 O 3 OC. Li, Na and K were identified as the optimal dopants. A quick screening of promising dopants for Fe 2 O 3 OC could be realized by our DFT calculations.

中文翻译：

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提高碱掺杂 Fe2O3 氧载体化学循环制氢反应活性的密度泛函理论研究

摘要 阻碍化学循环制氢广泛使用的主要障碍是高性能氧载体（OC）材料的稀缺性。在这里，我们首次通过密度泛函理论 (DFT) 计算研究了所有碱掺杂 Fe 2 O 3 OC 的反应性提高。首先，研究了碱性掺杂剂（Li、Na、K、Rb 和 Cs）在 Fe 2 O 3 晶体结构中的位置。我们的计算结果表明，所有的碱掺杂剂更倾向于位于 Fe 2 O 3 的表面而不是体中。然后通过DFT计算Fe 2 O 3 和碱掺杂Fe 2 O 3 OCs的氧空位形成能(E vac )，可用于评估OC表面氧的活性。发现所有碱掺杂Fe 2 O 3 与掺杂剂相邻的表面氧的E vac 远低于未掺杂Fe 2 O 3 的E vac 。离子半径越小，电负性越强，表面氧远离掺杂剂的E vac 越低。与远离掺杂剂的表面氧相比，靠近掺杂剂的表面氧将显示出更好的活性。最后，我们分析了碱掺杂剂对 Fe 2 O 3 OC 反应性的影响。我们得出结论，Li、Na和K掺杂剂的加入肯定能够增强表面氧的活性，从而提高Fe 2 O 3 OC的反应性。与Li、Na和K相比，Rb和Cs对Fe 2 O 3 OC的反应性有更差的协同作用。Li、Na 和 K 被确定为最佳掺杂剂。