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The breaking of nonpolar N≡N bond of dinitrogen is the biggest dilemma for electrocatalytic nitrogen reduction reaction (NRR) application, driving electron migration between catalysts and N≡N bond (termed “π back-donation” process) is crucial for attenuating interfacial energy barrier but still remains challenging. Herein, using density functional theory calculations, we revealed that constructing a unique hetero-dicationic Mo4+–Mo6+ pair could effectively activate N≡N bond with a lying-down chemisorption configuration by an asymmetrical “π back-donation” process. As a proof-of-concept demonstration, we synthesized MoO2@MoO3 heterostructure with double Mo sites (Mo4+–Mo6+), which are embedded in graphite, for electrochemical nitrogen reduction. Impressively, this hetero-dicationic Mo4+–Mo6+ pair catalysts display more excellent catalytic performance with a high NH3 yield (60.9 µg·h−1·mg−1) and Faradic efficiency (23.8%) as NRR catalysts under ambient conditions than pristine MoO2 and MoO3. Operando characterizations using synchrotron-based spectroscopic techniques identified the emergence of a key *N2Hy intermediate on Mo sites during NRR, which indicates that the Mo sites are active sites and the NRR process tends to follow an associative mechanism. This novel type of hetero-dicationic catalyst has tremendous potential as a new class of transition metal-based catalysts with promising applications in electrocatalysis and catalysts for energy conversion and storage.

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Publication history

Received: 14 September 2021
Revised: 11 October 2021
Accepted: 12 October 2021
Published: 06 November 2021
Issue date: September 2021

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© Tsinghua University Press and Springer-Verlag GmbH Germany, part of Springer Nature 2021

Acknowledgements

Acknowledgements

This work was financially supported by the National Natural Science Foundation of China (Nos. 11975234, 11775225, 12075243, and 12005227), the Users with Excellence Program of Hefei Science Center CAS (Nos. 2021HSC-UE002, 2020HSC-UE002, and 2019HSC-UE002), the Innovative Program of Development Foundation of Hefei Center for Physical Science and Technology (No. 2020HSC-CIP013), the Postdoctoral Science Foundation of China (Nos. 2019M662202, 2020M682041, and 2020TQ0316), the Fundamental Research Funds for the Central Universities (No. WK2310000103), The support from the Ministry of Science and Technology of China (No. 2017YFA0204904) is gratefully acknowledged. The numerical calculations in this paper have been done on the supercomputing system in the Supercomputing Center of University of Science and Technology of China. This work was partially carried out at the USTC Center for Micro and Nanoscale Research and Fabrication. The authors would like to thank BSRF, SSRF and NSRL for the synchrotron beamtime.

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Email: nanores@tup.tsinghua.edu.cn

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