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Due to the high specific surface area, abundant nitrogen and micropores, ZIF-8 is a commonly used precursor for preparing high performance Fe-N-C catalysts. However, the Zn element is inevitably remained in the prepared Fe-N-C catalyst. Whether the residual Zn element affects the catalytic activity and active site center of the Fe-N-C catalyst caused widespread curiosity, but has not been studied yet. Herein, we built several Fe, Zn, and N co-doped graphene models to investigate the effect of Zn atoms on the electrocatalytic performance of Fe-N-C catalysts by using density functional theory method. The calculation results show that all the calculated Fe-Zn-Nx structures are thermodynamically stable due to the negative formation energies and relative stabilities. The active sites around Fe and Zn atoms in the structure of Fe-Zn-N6(III) show the lowest oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) overpotentials of 0.38 and 0.43 V, respectively. The bridge site of Fe-Zn in Fe-Zn-N5 shows the lowest η HER of −0.26 V. A few structures with a better activity than that of FeN4 or ZnN4 are attributed to the synergistic effects between Fe and Zn atoms. The calculated ORR reaction pathways on Fe-Zn-N6(III) show that H2O is the final product and the ORR mechanism on the catalyst would be a four-electron process, and the existence of Zn element in the Fe-N-C catalysts plays a key role in reducing the ORR activation energy barrier. The results are helpful for the deep understand of high-performance Fe-N-C catalysts.

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Publication history

Received: 22 July 2020
Revised: 21 August 2020
Accepted: 23 August 2020
Published: 01 March 2021
Issue date: March 2021

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© Tsinghua University Press and Springer-Verlag GmbH Germany, part of Springer Nature

Acknowledgements

The authors acknowledge the financial support from the National Natural Science Foundation of China (Nos. 21673014 and 21975010). This research is supported by the high- performance computing (HPC) resources at Beihang University. The work is carried out at LvLiang Cloud Computing Center of China, and the calculations are performed on TianHe-2.

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Email: nanores@tup.tsinghua.edu.cn

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