Synthetic manganese–calcium oxides mimic the water-oxidizing complex of photosynthesis functionally and structurally

Zaharieva, Ivelina; Najafpour, Mohammad Mahdi; Wiechen, Mathias; Haumann, Michael; Kurz, Philipp; Dau, Holger

doi:10.1039/c0ee00815j

Cited by 266 publications

(390 citation statements)

References 73 publications

(115 reference statements)

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“…29 Well-ordered, microcrystalline Mn oxides generally may be largely inactive in water oxidation. 15,61 The prevalence of coordinatively saturated m 3-5 -oxo bonds and the absence of terminal coordination sites for water binding appear to preclude water-oxidation activity in both well ordered colloidal (see ref. 61) and electrodeposited Mn oxides.…”

Section: Structure-function Relationmentioning

confidence: 99%

“…15,61 The prevalence of coordinatively saturated m 3-5 -oxo bonds and the absence of terminal coordination sites for water binding appear to preclude water-oxidation activity in both well ordered colloidal (see ref. 61) and electrodeposited Mn oxides. In conclusion, we propose that the relatively high extent of order in the Mn oxides deposited at constant potential is the cause for their comparatively low activity.…”

Section: Structure-function Relationmentioning

confidence: 99%

“…It is conceivable that, in the MnCat, Mn ions attached by monom-oxo bridges replace Ca with respect to its structural role in the photosynthetic Mn 4 Ca complex and in Mn 2 Ca-oxide particles. 61 Bridging oxides likely are mechanistically pivotal in biological water oxidation. 8,[62][63][64] Also in synthetic water-oxidizing oxides, extensive di-m-oxo bridging between redox-active metal ions emerges as a key motif.…”

Section: Structure-function Relationmentioning

confidence: 99%

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Electrosynthesis, functional, and structural characterization of a water-oxidizing manganese oxide

Zaharieva

Chernev

Risch

et al. 2012

Energy Environ. Sci.

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413

583

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In the sustainable production of non-fossil fuels, water oxidation is pivotal. Development of efficient catalysts based on manganese is desirable because this element is earth-abundant, inexpensive, and largely non-toxic. We report an electrodeposited Mn oxide (MnCat) that catalyzes electrochemical water oxidation at neutral pH at rates that approach the level needed for direct coupling to photoactive materials. By choice of the voltage protocol we could switch between electrodeposition of inactive Mn oxides (deposition at constant anodic potentials) and synthesis of the active MnCat (deposition by voltage-cycling protocols). Electron microscopy reveals that the MnCat consists of nanoparticles (100 nm) with complex fine-structure. X-ray spectroscopy reveals that the amorphous MnCat resembles the biological paragon, the water-splitting Mn 4 Ca complex of photosynthesis, with respect to mean Mn oxidation state (ca. +3.8 in the MnCat) and central structural motifs. Yet the MnCat functions without calcium or other bivalent ions. Comparing the MnCat with electrodeposited Mn oxides inactive in water oxidation, we identify characteristics that likely are crucial for catalytic activity. In both inactive Mn oxides and active ones (MnCat), extensive di-m-oxo bridging between Mn ions is observed. However in the MnCat, the voltage-cycling protocol resulted in formation of Mn III sites and prevented formation of well-ordered and unreactive Mn IV O 2 . Structure-function relations in Mn-based wateroxidation catalysts and strategies to design catalytically active Mn-based materials are discussed. Knowledge-guided performance optimization of the MnCat could pave the road for its technological use. Broader contextThreatening global climate changes and unsecured supply of fossil fuels call for a global transition toward sustainable energyconversion systems. The storage of wind or solar energy by formation of energy-rich fuel molecules could play a central role in both transient storage of the intermittently provided energy and replacement of fossil fuels in the transportation sector. Whether hydrogen or a carbon-based fuel is the target, in any event the extraction of reducing equivalents and protons from water (that is, water oxidation) is pivotal. In search of water-oxidation catalysts that ultimately could play a role at a global scale, we and others are aiming at development of simple routes towards formation of Mn-based catalysts. Manganese excels by high availability and low toxicity; and in oxygenic photosynthesis, nature has demonstrated that a Mn-based catalyst can oxidize water efficiently. When aiming at an 'artificial leaf' with a Mn-based catalyst directly coupled to a solar-energy-converting material, the activity of the catalyst (per area) needs to cope with the incoming photon flux. Moreover the device design typically requires the use of benign synthesis and operation conditions, that is, temperatures close to room temperature and pH close to neutral. As an important first step, we report a simple protocol for e...

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Section: Structure-function Relationmentioning

confidence: 99%

Section: Structure-function Relationmentioning

confidence: 99%

Section: Structure-function Relationmentioning

confidence: 99%

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Electrosynthesis, functional, and structural characterization of a water-oxidizing manganese oxide

Zaharieva

Chernev

Risch

et al. 2012

Energy Environ. Sci.

Self Cite

413

583

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“…[8][9][10][11][12][13][14] Severals tudies have shown that amorphous, layered manganese oxides from the birnessite mineral family are the mostp romising preciousmetal-free OER catalysts, especially for neutral and acidic reaction media. [8,13,15,16] Birnessites consist of layers of edge-sharing [MnO 6 ]o ctahedra with MnÀOa nd MnÀMn distances of approximately 1.9 and 2.9 ,respectively.The distance between two layers is approximately 7 andt he interlayer space can contain varying amountso fw ater and/or additional cations (especially of alkali and earth alkali metals).…”

Section: Introductionmentioning

confidence: 99%

Electrocatalytic Water Oxidation by MnO_x/C: In Situ Catalyst Formation, Carbon Substrate Variations, and Direct O₂/CO₂ Monitoring by Membrane‐Inlet Mass Spectrometry

et al. 2017

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Layers of amorphous manganese oxides were directly formed on the surfaces of different carbon materials by exposing the carbon to aqueous solutions of permanganate (MnO4−) followed by sintering at 100–400 °C. During electrochemical measurements in neutral aqueous buffer, nearly all of the MnOx/C electrodes show significant oxidation currents at potentials relevant for the oxygen evolution reaction (OER). However, by combining electrolysis with product detection by using mass spectrometry, it was found that these currents were only strictly linked to water oxidation if MnOx was deposited on graphitic carbon materials (faradaic O2 yields >90 %). On the contrary, supports containing sp3‐C were found to be unsuitable as the OER is accompanied by carbon corrosion to CO2. Thus, choosing the “right” carbon material is crucial for the preparation of stable and efficient MnOx/C anodes for water oxidation catalysis. For MnOx on graphitic substrates, current densities of >1 mA cm−2 at η=540 mV could be maintained for at least 16 h of continuous operation at pH 7 (very good values for electrodes containing only abundant elements such as C, O, and Mn) and post‐operando measurements proved the integrity of both the catalyst coating and the underlying carbon at OER conditions.

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“…The challenge is to have a molecular arrangement such that the artificial catalysts efficiently use light energy to split water and concomitantly provide reducing potential for hydrogen gas production or CO 2 reduction. It has been demonstrated that catalysts based on Mn or Mn doped with Ca are capable of water splitting and generating dioxygen (Limberg et al 1999;Tagore et al 2008;Najafpour et al 2010;Zaharieva et al 2011;Gao et al 2012). Frei and coworkers (Jiao and Frei 2010) reported that nanostructured manganese oxide clusters supported on mesoporous silica efficiently evolved oxygen in aqueous solution under mild conditions.…”

Section: Artificial Photosynthesismentioning

confidence: 99%

Photosystem II: The Water-Splitting Enzyme of Photosynthesis

Barber

2012

Cold Spring Harbor Symposia on Quantitative Biology

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The oxygen in our atmosphere is derived and maintained by the water-splitting process of photosynthesis. The enzyme that facilitates this reaction and therefore underpins virtually all life on our planet is known as photosystem II (PSII), a multisubunit enzyme embedded in the lipid environment of the thylakoid membranes of plants, algae, and cyanobacteria. During the past 10 years, crystal structures of a 700-kDa cyanobacterial dimeric PSII complex have been reported with ever-increasing improvement in resolution-the latest at 1.9 Å . Thus, the organizational and structural details of its many subunits and cofactors are now well understood. The water-splitting site was revealed as a cluster of four Mn ions and one Ca ion surrounded by aminoacid side chains, of which seven provide ligands to the metals. The metal cluster is organized as a cubane-like structure composed of three Mn ions and the one Ca 2þ ion linked by oxo bonds. The fourth Mn is attached to the cubane via one of its bridging oxygens together with another oxo bridge to an Mn ion of the cubane. The overall structure of the catalytic site provides a framework to propose a mechanistic scheme for the water-splitting process and gives a blueprint for the development of catalysts that mimick the reaction in an artificial chemical system as a means to generate solar fuels.

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Synthetic manganese–calcium oxides mimic the water-oxidizing complex of photosynthesis functionally and structurally

Cited by 266 publications

References 73 publications

Electrosynthesis, functional, and structural characterization of a water-oxidizing manganese oxide

Electrosynthesis, functional, and structural characterization of a water-oxidizing manganese oxide

Electrocatalytic Water Oxidation by MnO_x/C: In Situ Catalyst Formation, Carbon Substrate Variations, and Direct O₂/CO₂ Monitoring by Membrane‐Inlet Mass Spectrometry

Photosystem II: The Water-Splitting Enzyme of Photosynthesis

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Synthetic manganese–calcium oxides mimic the water-oxidizing complex of photosynthesis functionally and structurally

Cited by 266 publications

References 73 publications

Electrosynthesis, functional, and structural characterization of a water-oxidizing manganese oxide

Electrosynthesis, functional, and structural characterization of a water-oxidizing manganese oxide

Electrocatalytic Water Oxidation by MnOx/C: In Situ Catalyst Formation, Carbon Substrate Variations, and Direct O2/CO2 Monitoring by Membrane‐Inlet Mass Spectrometry

Photosystem II: The Water-Splitting Enzyme of Photosynthesis

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Electrocatalytic Water Oxidation by MnO_x/C: In Situ Catalyst Formation, Carbon Substrate Variations, and Direct O₂/CO₂ Monitoring by Membrane‐Inlet Mass Spectrometry