Enhancing Catalytic Activity by Narrowing Local Energy Gaps—X‐Ray Studies of a Manganese Water Oxidation Catalyst

Xiao, Jie; Khan, Munirah; Singh, Archana; Suljoti, Edlira; Spiccia, Leone; Aziz, Emad F.

doi:10.1002/cssc.201403219

Cited by 7 publications

(21 citation statements)

References 45 publications

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“…More recently, based on the results obtained from a combination of XAS and RIXS, Xiao et al suggested that enhancement in water oxidation catalytic activity originated from a narrowing of the local HOMO-LUMO gap when potential and visible light illumination were simultaneously applied to a dinuclear Mn 3+ system. 104 RIXS experiments were also performed by Khan and coworkers (2014) on MnO x nanoparticles loaded into Nafion, indicating that the MnO x catalyst with the lowest d-d transitions and the strongest charge transfer showed the highest catalytic activity. 81 Bokarev et al studied the difference in the behaviour of the different oxidation states of manganese regarding the photo-electrooxidation of water.…”

Section: Soft X-ray Investigations: O K-edge M L-edge and Rixsmentioning

confidence: 89%

In situ X-ray absorption spectroscopy of transition metal based water oxidation catalysts

et al. 2017

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X-ray absorption studies of the geometric and electronic structure of primarily heterogeneous Co, Ni, and Mn based water oxidation catalysts are reviewed. The X-ray absorption near edge and extended X-ray absorption fine structure studies of the metal K-edge, characterize the metal oxidation state, metal-oxygen bond distance, metal-metal distance, and degree of disorder of the catalysts. These properties guide the coordination environment of the transition metal oxide radical that localizes surface holes and is required to oxidize water. The catalysts are investigated both as-prepared, in their native state, and under reaction conditions, while transition metal oxide radicals are generated. The findings of many experiments are summarized in tables. The advantages of future X-ray experiments on water oxidation catalysts, which include the limited data available of the oxygen K-edge, metal L-edge, and resonant inelastic X-ray scattering, are discussed.

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Section: Soft X-ray Investigations: O K-edge M L-edge and Rixsmentioning

confidence: 89%

In situ X-ray absorption spectroscopy of transition metal based water oxidation catalysts

et al. 2017

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“…[21,22] Probing the valence states at specific catalytic sites is particularly desirable since they are very sensitivet ot he oxidation state of the element of interest and its surrounding chemical environment (ligandf ield);i ti s, therefore, possible to uncover details aboutthe mechanism of catalysis.…”

Section: Introductionmentioning

confidence: 99%

On the Origin of the Improvement of Electrodeposited MnO_x Films in Water Oxidation Catalysis Induced by Heat Treatment

et al. 2015

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Manganese oxides (MnOx ) are considered to be promising catalysts for water oxidation. Building on our previous studies showing that the catalytic activity of MnOx films electrodeposited from aqueous electrolytes is improved by a simple heat treatment, we have explored the origin of the catalytic enhancement at an electronic level by X-ray absorption spectroscopy (XAS). The Mn L-edge XA spectra measured at various heating stages were fitted by linear combinations of the spectra of the well-defined manganese oxides-MnO, Mn3 O4 , Mn2 O3 , MnO2 and birnessite. This analysis identified two major manganese oxides, Mn3 O4 and birnessite, that constitute 97 % of the MnOx films. Moreover, the catalytic improvement on heat treatment at 90 °C is related to the conversion of a small amount of birnessite to the Mn3 O4 phase, accompanied by an irreversible dehydration process. Further dehydration at higher temperature (120 °C), however, leads to a poorer catalytic performance.

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“…The details for the experimental results discussed in the present work are reported elsewhere. 22,23 Page 8 of 33…”

Section: Computational Detailsmentioning

confidence: 99%

“…22,23 These manganese-based nanostructured catalysts are exploiting the similarity to the natural water-oxidation systems 24,25 and have attracted much attention. [24][25][26][27][28][29] The L-edge X-ray spectroscopy revealed the important role of the Mn III oxidation state and correlation of the local HOMO-LUMO gap at the Mn sites with the catalytic activity.…”

Section: Introductionmentioning

confidence: 99%

“…[24][25][26][27][28][29] The L-edge X-ray spectroscopy revealed the important role of the Mn III oxidation state and correlation of the local HOMO-LUMO gap at the Mn sites with the catalytic activity. 22,23 In view of these experimental findings, the purpose of this article is twofold. First, since the catalytic activity is sensitive to the oxidation state of Mn ions, 22,23,25,29 the detailed assignment of spectral features of manganese in different oxidation states is warrant.…”

Section: Introductionmentioning

confidence: 99%

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Unraveling the Electronic Structure of Photocatalytic Manganese Complexes by L-Edge X-ray Spectroscopy

et al. 2015

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X-ray absorption (XAS) and resonant inelastic scattering (RIXS) of a number of Mn 2+,3+,4+ complexes relevant for photo-electrooxidation of water is studied theoretically using the RASSCF/RASSI approach. This enables us to quantify spin-orbit coupling induced mixing of states with different multiplicities in the valence-and core-excited electronic states, evidencing the mostly spin-forbidden character of transitions in RIXS spectra. The notably different patterns of spectroscopic features in this series of substances not only provide insight into their electronic structure, but open the possibility for tracing redox evolution by means of X-ray spectroscopy.Specific findings deduced from the analysis of the shape of the RIXS spectra concern the gap between the ground and first excited valence states relevant for catalytic activity. This gap is substantially lower for Mn 3+ as compared to the even oxidation states.

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Enhancing Catalytic Activity by Narrowing Local Energy Gaps—X‐Ray Studies of a Manganese Water Oxidation Catalyst

Cited by 7 publications

References 45 publications

In situ X-ray absorption spectroscopy of transition metal based water oxidation catalysts

In situ X-ray absorption spectroscopy of transition metal based water oxidation catalysts

On the Origin of the Improvement of Electrodeposited MnO_x Films in Water Oxidation Catalysis Induced by Heat Treatment

Unraveling the Electronic Structure of Photocatalytic Manganese Complexes by L-Edge X-ray Spectroscopy

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Enhancing Catalytic Activity by Narrowing Local Energy Gaps—X‐Ray Studies of a Manganese Water Oxidation Catalyst

Cited by 7 publications

References 45 publications

In situ X-ray absorption spectroscopy of transition metal based water oxidation catalysts

In situ X-ray absorption spectroscopy of transition metal based water oxidation catalysts

On the Origin of the Improvement of Electrodeposited MnOx Films in Water Oxidation Catalysis Induced by Heat Treatment

Unraveling the Electronic Structure of Photocatalytic Manganese Complexes by L-Edge X-ray Spectroscopy

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On the Origin of the Improvement of Electrodeposited MnO_x Films in Water Oxidation Catalysis Induced by Heat Treatment