Spectroscopic capture of a low-spin Mn(IV)-oxo species in Ni-Mn3O4 nanoparticles during water oxidation catalysis
- Authors
- Park, Sunghak; Jin, Kyoungsuk; Lim, Hyung Kyu; Kim, Jin; Cho, Kang Hee; Choi, Seungwoo; Seo, Hongmin; Lee, Moo Young; Lee, Yoon Ho; Yoon, Sangmoon; Kim, Miyoung; Kim, Hyungjun; Kim, Sun Hee; Nam, Ki Tae
- Issue Date
- Oct-2020
- Publisher
- NATURE RESEARCH
- Citation
- NATURE COMMUNICATIONS, v.11, no.1
- Journal Title
- NATURE COMMUNICATIONS
- Volume
- 11
- Number
- 1
- URI
- https://scholarworks.bwise.kr/gachon/handle/2020.sw.gachon/83610
- DOI
- 10.1038/s41467-020-19133-w
- ISSN
- 2041-1723
- Abstract
- High-valent metal-oxo moieties have been implicated as key intermediates preceding various oxidation processes. The critical O-O bond formation step in the Kok cycle that is presumed to generate molecular oxygen occurs through the high-valent Mn-oxo species of the water oxidation complex, i.e., the Mn4Ca cluster in photosystem II. Here, we report the spectroscopic characterization of new intermediates during the water oxidation reaction of manganese-based heterogeneous catalysts and assign them as low-spin Mn(IV)-oxo species. Recently, the effects of the spin state in transition metal catalysts on catalytic reactivity have been intensely studied; however, no detailed characterization of a low-spin Mn(IV)-oxo intermediate species currently exists. We demonstrate that a low-spin configuration of Mn(IV), S=1/2, is stably present in a heterogeneous electrocatalyst of Ni-doped monodisperse 10-nm Mn3O4 nanoparticles via oxo-ligand field engineering. An unprecedented signal (g=1.83) is found to evolve in the electron paramagnetic resonance spectrum during the stepwise transition from the Jahn-Teller-distorted Mn(III). In-situ Raman analysis directly provides the evidence for Mn(IV)-oxo species as the active intermediate species. Computational analysis confirmed that the substituted nickel species induces the formation of a z-axis-compressed octahedral C-4v crystal field that stabilizes the low-spin Mn(IV)-oxo intermediates. Understanding reaction intermediates provides a foundation for active electrocatalysts' design, but it remains elusive for heterogeneous electrocatalysts. Here, the authors report the spectroscopic characterization of low-spin Mn(IV)-oxo as the active intermediates during electrochemical water oxidation.
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