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Nanomaterials 2019, 9(4), 577; https://doi.org/10.3390/nano9040577

Direct Spectroscopy for Probing the Critical Role of Partial Covalency in Oxygen Reduction Reaction for Cobalt-Manganese Spinel Oxides

1,2,3, 1,2, 1,2, 4, 5, 1,2,3, 1,2,3, 1,2,6, 4 and 1,2,6,*
1
State Key Laboratory of Functional Materials for Informatics, Shanghai Institute of Microsystem and Information Technology, Chinese Academy of Sciences, Shanghai 200050, China
2
CAS Center for Excellence in Superconducting Electronics (CENSE), Chinese Academy of Sciences, Shanghai 200050, China
3
University of Chinese Academy of Sciences, Beijing 100049, China
4
Key Laboratory of Advanced Energy Materials Chemistry (Ministry of Education) and State Key Laboratory of Elemento-Organic Chemistry, College of Chemistry, Nankai University, Tianjin 300071, China
5
Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA
6
School of Physical Science and Technology, Shanghai Tech University, Shanghai 200031, China
*
Author to whom correspondence should be addressed.
Received: 25 February 2019 / Revised: 30 March 2019 / Accepted: 1 April 2019 / Published: 9 April 2019
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Abstract

Nanocrystalline multivalent metal spinels are considered as attractive non-precious oxygen electrocatalysts. Identifying their active sites and understanding their reaction mechanisms are essential to explore novel transition metal (TM) oxides catalysts and further promote their catalytic efficiency. Here we report a systematic investigation, by means of soft X-ray absorption spectroscopy (sXAS), on cubic and tetragonal CoxMn3-xO4 (x = 1, 1.5, 2) spinel oxides as a family of highly active catalysts for the oxygen reduction reaction (ORR). We demonstrate that the ORR activity for oxide catalysts primarily correlates to the partial covalency of between O 2p orbital with Mn4+ 3d t2g-down/eg-up, Mn3+ 3d eg-up and Co3+ 3d eg-up orbitals in octahedron, which is directly revealed by the O K-edge sXAS. Our findings propose the critical influences of the partial covalency between oxygen 2p band and specific metal 3d band on the competition between intermediates displacement of the ORR, and thus highlight the importance of electronic structure in controlling oxide catalytic activity. View Full-Text
Keywords: oxygen reduction reaction; spinel oxides; soft X-ray absorption spectroscopy; partial covalency; catalytic activity oxygen reduction reaction; spinel oxides; soft X-ray absorption spectroscopy; partial covalency; catalytic activity
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Long, X.; Yu, P.; Zhang, N.; Li, C.; Feng, X.; Ren, G.; Zheng, S.; Fu, J.; Cheng, F.; Liu, X. Direct Spectroscopy for Probing the Critical Role of Partial Covalency in Oxygen Reduction Reaction for Cobalt-Manganese Spinel Oxides. Nanomaterials 2019, 9, 577.

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