Manganese Dioxide as Specific Redox Catalyst in the Photosensitized Oxygen Generation From Water

Okuno, Yohmei; Yonemitsu, Osamu; Chiba, Yukihiro

doi:10.1246/cl.1983.815

Cited by 39 publications

(14 citation statements)

References 6 publications

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“…Taking early studies of electro-or photon-driven Co and Mn oxide catalysts as point of departure [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16], development of nanostructured forms of these oxides featuring very high surface areas have dramatically increased turnover frequencies of O 2 product formation per projected catalyst area [17][18][19]. The need for high turnover frequency per projected area in artificial photosynthesis is based on the requirement that the catalyst should keep up with the incident solar flux in order to minimize wasting of photons.…”

Section: Introductionmentioning

confidence: 99%

Towards a Molecular Level Understanding of the Multi-Electron Catalysis of Water Oxidation on Metal Oxide Surfaces

Zhang

Frei

2014

Catal Lett

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Earth abundant metal oxides play a central role as catalysts in the essential chemical transformations of sunlight to fuel conversion, which are the oxidation of water and the reduction of carbon dioxide. The rapidly growing interest in renewable fuel generation by using the energy of the sun has recently led to substantial breakthroughs in the use of first row transition metal oxides as catalysts for oxygen evolution from water. Substantive improvements of rates and lowering of overpotentials have been achieved by exploiting materials properties on the nanoscale, or taking advantage of the synergy of multiple metals. Moreover, knowledge derived from mechanistic investigations with structure specific spectroscopy is accelerating efficiency improvements. Monitoring by timeresolved FT-infrared spectroscopy reveals the molecular nature of active sites, while in situ X-ray and optical spectroscopy under reaction conditions provides insights into the electronic structure of the surface metal centers participating in the catalysis. By combining the bond specificity of vibrational spectroscopy with the metal electronic structure specificity of optical, X-ray absorption or photoelectron spectroscopy, a complete understanding of active surface sites on metal oxides begins to emerge. Charge flow driving the chemical transformations probed by optical spectroscopy across time scales from ultrafast to very slow reveals the processes that control the productive use of charges delivered to the catalyst. Coupling of the water oxidation catalysis at a metal oxide catalyst with carbon dioxide reduction at a heterobinuclear chromophore, which is the goal of the artificial photosystem approach, is demonstrated by a well-defined all-inorganic polynuclear unit.

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Section: Introductionmentioning

confidence: 99%

Towards a Molecular Level Understanding of the Multi-Electron Catalysis of Water Oxidation on Metal Oxide Surfaces

Zhang

Frei

2014

Catal Lett

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“…In ac- [50,89,90] as well as for the active biomimetic CaMn 2 O 4 ·H 2 O mineral phase (see Table S4 for comparison). [43] In fact, our results underline again that biomimicking heterogeneous manganese oxides can be highly efficient even in the absence of calcium or any other alkali and alkaline earth metals.…”

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confidence: 99%

Nanostructured Manganese Oxides as Highly Active Water Oxidation Catalysts: A Boost from Manganese Precursor Chemistry

et al. 2014

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We present a facile synthesis of bioinspired manganese oxides for chemical and photocatalytic water oxidation, starting from a reliable and versatile manganese(II) oxalate single-source precursor (SSP) accessible through an inverse micellar molecular approach. Strikingly, thermal decomposition of the latter precursor in various environments (air, nitrogen, and vacuum) led to the three different mineral phases of bixbyite (Mn2 O3 ), hausmannite (Mn3 O4 ), and manganosite (MnO). Initial chemical water oxidation experiments using ceric ammonium nitrate (CAN) gave the maximum catalytic activity for Mn2 O3 and MnO whereas Mn3 O4 had a limited activity. The substantial increase in the catalytic activity of MnO in chemical water oxidation was demonstrated by the fact that a phase transformation occurs at the surface from nanocrystalline MnO into an amorphous MnOx (1

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“…Arange of different types of manganese oxideshave already been tested for WOC, albeit rarely under identical experimental conditions. [6,8,12,13,[17][18][19][20][21][22][23] Instead, catalyst concentrations,o xidising agents, pH regime and so forth differedg reatly from study to study,a nd the reported WOC rates therefore can hardly be compared. To our knowledge, in only one report to date have WOC rates of more than three different types of manganese oxide been screened in the same catalysis set-up, namely,t he report by Robinson et al in 2013 on as et of crystalline MnO x compounds and their WOC performances.…”

Section: Introductionmentioning

confidence: 99%

“…Given this large variety of solid‐state structures and the known WOC activity of some manganese oxides, different factors have been suggested to be important for the catalytic process: 1) similar to the OEC, flexible structures should be beneficial for substrate binding and oxidation‐state changes,5, 9, 10, 12, 18 2) high surface areas result in good accessibility of the catalytically active centres,7, 12, 13, 19, 20, 25 3) average Mn oxidation states greater than +3.5 often provide enough thermodynamic driving force for water oxidation,7, 18, 22, 26 4) secondary cations such as (Lewis acidic) Ca 2+ assist water oxidation by activation of the H 2 O substrate10, 12, 13 and 5) good conductivity of the oxide enhances performance, because WOC requires that four oxidation equivalents accumulate at the (so far unidentified) catalytic sites in the MnO x 9. 18 Some of these factors are obviously contradictory to each other, and so there is currently no real consensus on the most important structural parameters influencing WOC activities of manganese oxides.…”

Section: Introductionmentioning

confidence: 99%

Water Oxidation Catalysis by Synthetic Manganese Oxides with Different Structural Motifs: A Comparative Study

Frey

Kurz

2015

Chemistry A European J

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Manganese oxides are considered to be very promising materials for water oxidation catalysis (WOC), but the structural parameters influencing their catalytic activity have so far not been clearly identified. For this study, a dozen manganese oxides (MnOx ) with various solid-state structures were synthesised and carefully characterised by various physical and chemical methods. WOC by the different MnOx was then investigated with Ce(4+) as chemical oxidant. Oxides with layered structures (birnessites) and those containing large tunnels (todorokites) clearly gave the best results with reaction rates exceeding 1250 ${{\rm{mmol}}_{{\rm{O}}_{\rm{2}} } }$ ${{\rm{mol}}_{{\rm{Mn}}}^{ - 1} }$ h(-1) or about 50 μmolO2 m(-2) h(-1) . In comparison, catalytic rates per mole of Mn of oxides characterised by well-defined 3D networks were rather low (e.g., ca. 90 ${{\rm{mmol}}_{{\rm{O}}_{\rm{2}} } }$ ${{\rm{mol}}_{{\rm{Mn}}}^{ - 1} }$ h(-1) for bixbyite, Mn2 O3 ), but impressive if normalised per unit surface area (>100 ${{\rm{{\rm \mu} mol}}_{{\rm{O}}_{\rm{2}} } }$ m(-2) h(-1) for marokite, CaMn2 O4 ). Thus, two groups of MnOx emerge from this screening as hot candidates for manganese-based WOC materials: 1) amorphous oxides with tunnelled structures and the well-established layered oxides; 2) crystalline Mn(III) oxides. However, synthetic methods to increase surface areas must be developed for the latter to obtain good catalysis rates per mole of Mn or per unit catalyst mass.

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Manganese Dioxide as Specific Redox Catalyst in the Photosensitized Oxygen Generation From Water

Cited by 39 publications

References 6 publications

Towards a Molecular Level Understanding of the Multi-Electron Catalysis of Water Oxidation on Metal Oxide Surfaces

Towards a Molecular Level Understanding of the Multi-Electron Catalysis of Water Oxidation on Metal Oxide Surfaces

Nanostructured Manganese Oxides as Highly Active Water Oxidation Catalysts: A Boost from Manganese Precursor Chemistry

Water Oxidation Catalysis by Synthetic Manganese Oxides with Different Structural Motifs: A Comparative Study

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