The Experts below are selected from a list of 276 Experts worldwide ranked by ideXlab platform
Suleyman I Allakhverdiev - One of the best experts on this subject based on the ideXlab platform.
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Manganese Compounds as water oxidizing catalysts from the natural water oxidizing complex to nanosized Manganese oxide structures
Chemical Reviews, 2016Co-Authors: Mohammad Mahdi Najafpour, G Renger, Malgorzata Holynska, Atefeh Nemati Moghaddam, Robert Carpentier, Hiroshi Nishihara, Julian J Eatonrye, Jianren Shen, Suleyman I AllakhverdievAbstract:All cyanobacteria, algae, and plants use a similar water-oxidizing catalyst for water oxidation. This catalyst is housed in Photosystem II, a membrane-protein complex that functions as a light-driven water oxidase in oxygenic photosynthesis. Water oxidation is also an important reaction in artificial photosynthesis because it has the potential to provide cheap electrons from water for hydrogen production or for the reduction of carbon dioxide on an industrial scale. The water-oxidizing complex of Photosystem II is a Mn–Ca cluster that oxidizes water with a low overpotential and high turnover frequency number of up to 25–90 molecules of O2 released per second. In this Review, we discuss the atomic structure of the Mn–Ca cluster of the Photosystem II water-oxidizing complex from the viewpoint that the underlying mechanism can be informative when designing artificial water-oxidizing catalysts. This is followed by consideration of functional Mn-based model complexes for water oxidation and the issue of Mn com...
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nano sized Manganese oxides as biomimetic catalysts for water oxidation in artificial photosynthesis a review
Journal of the Royal Society Interface, 2012Co-Authors: Mohammad Mahdi Najafpour, Fahimeh Rahimi, Suleyman I AllakhverdievAbstract:There has been a tremendous surge in research on the synthesis of various metal Compounds aimed at simulating the water-oxidizing complex (WOC) of photosystem II (PSII). This is crucial because the water oxidation half reaction is overwhelmingly rate-limiting and needs high over-voltage (approx. 1 V), which results in low conversion efficiencies when working at current densities required for hydrogen production via water splitting. Particular attention has been given to the Manganese Compounds not only because Manganese has been used by nature to oxidize water but also because Manganese is cheap and environmentally friendly. The Manganese–calcium cluster in PSII has a dimension of about approximately 0.5 nm. Thus, nano-sized Manganese Compounds might be good structural and functional models for the cluster. As in the nanometre-size of the synthetic models, most of the active sites are at the surface, these Compounds could be more efficient catalysts than micrometre (or bigger) particles. In this paper, we focus on nano-sized Manganese oxides as functional and structural models of the WOC of PSII for hydrogen production via water splitting and review nano-sized Manganese oxides used in water oxidation by some research groups.
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Manganese Compounds as water oxidizing catalysts for hydrogen production via water splitting from Manganese complexes to nano sized Manganese oxides
International Journal of Hydrogen Energy, 2012Co-Authors: Mohammad Mahdi Najafpour, Suleyman I AllakhverdievAbstract:Abstract For hydrogen production by water splitting, the water oxidation half reaction is overwhelmingly rate limiting and needs high over-voltage (∼1 V), which results in low conversion efficiencies when working at current densities required. At this high voltage, other chemicals will be also oxidized and this would be environmentally unacceptable for large-scale H2 production. In past few years, there has been a tremendous surge in research on the synthesis of various metal Compounds aimed at the simulating water oxidizing complex of Photosystem II. Particular attention has been given to the Manganese Compounds not only because Manganese has been used by Nature to oxidize water but also because Manganese is cheap and environmentally friendly. In this review, we focus on Manganese Compounds as functional models of the water oxidizing complex of Photosystem II for hydrogen production via water splitting.
K H J Buschow - One of the best experts on this subject based on the ideXlab platform.
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Magnetic properties of rare earth-Manganese Compounds of the type RMnSi2
Journal of Alloys and Compounds, 1994Co-Authors: Penelope Schobinger-papamantellos, J H V J Brabers, F R De Boer, K H J BuschowAbstract:Abstract We have studied the temperature dependence of the intrinsic coercivity of the Compounds RMnSi 2 (R La, Ce, Pr, Nd) from 4.2 to 300 K. The differences in coercivity behaviour observed for these Compounds were correlated with the corresponding temperature behaviour of the magnetic structures and with the valence instability of Ce in CeMnSi 2 . Magnetic isotherms of LaMnSi 2 and CeMnSi 2 at 4.2 K were studied in field strengths up to 35 T. Neutron diffraction measurements were performed on CeMnSi 2 at 8 and 408 K. From the results of neutron diffraction and high field measurements it was concluded that Ce loses its magnetic moment at low temperatures. This is the first example of a strongly ferromagnetic compound in which Ce has an unstable valence.
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magnetic properties of rare earth Manganese Compounds of the rmn6ge6 type
Journal of Alloys and Compounds, 1993Co-Authors: J H V J Brabers, V H M Duijn, F R De Boer, K H J BuschowAbstract:Abstract We determined the magnetic properties of several Compounds of the type RMn 6 Ge 6 (R is a heavy rare-earth element). Several of these Compounds give rise to two ordering temperatures associated with antiferromagnetic ordering of the R and Mn sublattices. For GdMn 6 Sn 6 and to some extent also for TbMn 6 Sn 6 we observed magnetic behaviour which can be described as “bootstrap ferrimagnetism”: the antiferromagnetic configurations within both the R and Mn sublattices are broken simultaneously by the R-Mn intersublattice interaction, leading to ferrimagnetic alignment of the R and Mn sublattices. This bootstrap mechanism is sufficiently strong only if the intrasublattice Mn-Mn interaction is sufficiently weak. This condition is met only when the unit cell volume is sufficiently large. The interplay between intersublattice coupling and unit cell volume leads to interesting temperature dependences of the magnetization. In the magnetic isotherms the bootstrap mechanism leads to first-order phase transitions.
Mohammad Mahdi Najafpour - One of the best experts on this subject based on the ideXlab platform.
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Manganese Compounds as water oxidizing catalysts from the natural water oxidizing complex to nanosized Manganese oxide structures
Chemical Reviews, 2016Co-Authors: Mohammad Mahdi Najafpour, G Renger, Malgorzata Holynska, Atefeh Nemati Moghaddam, Robert Carpentier, Hiroshi Nishihara, Julian J Eatonrye, Jianren Shen, Suleyman I AllakhverdievAbstract:All cyanobacteria, algae, and plants use a similar water-oxidizing catalyst for water oxidation. This catalyst is housed in Photosystem II, a membrane-protein complex that functions as a light-driven water oxidase in oxygenic photosynthesis. Water oxidation is also an important reaction in artificial photosynthesis because it has the potential to provide cheap electrons from water for hydrogen production or for the reduction of carbon dioxide on an industrial scale. The water-oxidizing complex of Photosystem II is a Mn–Ca cluster that oxidizes water with a low overpotential and high turnover frequency number of up to 25–90 molecules of O2 released per second. In this Review, we discuss the atomic structure of the Mn–Ca cluster of the Photosystem II water-oxidizing complex from the viewpoint that the underlying mechanism can be informative when designing artificial water-oxidizing catalysts. This is followed by consideration of functional Mn-based model complexes for water oxidation and the issue of Mn com...
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nano sized Manganese oxides as biomimetic catalysts for water oxidation in artificial photosynthesis a review
Journal of the Royal Society Interface, 2012Co-Authors: Mohammad Mahdi Najafpour, Fahimeh Rahimi, Suleyman I AllakhverdievAbstract:There has been a tremendous surge in research on the synthesis of various metal Compounds aimed at simulating the water-oxidizing complex (WOC) of photosystem II (PSII). This is crucial because the water oxidation half reaction is overwhelmingly rate-limiting and needs high over-voltage (approx. 1 V), which results in low conversion efficiencies when working at current densities required for hydrogen production via water splitting. Particular attention has been given to the Manganese Compounds not only because Manganese has been used by nature to oxidize water but also because Manganese is cheap and environmentally friendly. The Manganese–calcium cluster in PSII has a dimension of about approximately 0.5 nm. Thus, nano-sized Manganese Compounds might be good structural and functional models for the cluster. As in the nanometre-size of the synthetic models, most of the active sites are at the surface, these Compounds could be more efficient catalysts than micrometre (or bigger) particles. In this paper, we focus on nano-sized Manganese oxides as functional and structural models of the WOC of PSII for hydrogen production via water splitting and review nano-sized Manganese oxides used in water oxidation by some research groups.
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Manganese Compounds as water oxidizing catalysts for hydrogen production via water splitting from Manganese complexes to nano sized Manganese oxides
International Journal of Hydrogen Energy, 2012Co-Authors: Mohammad Mahdi Najafpour, Suleyman I AllakhverdievAbstract:Abstract For hydrogen production by water splitting, the water oxidation half reaction is overwhelmingly rate limiting and needs high over-voltage (∼1 V), which results in low conversion efficiencies when working at current densities required. At this high voltage, other chemicals will be also oxidized and this would be environmentally unacceptable for large-scale H2 production. In past few years, there has been a tremendous surge in research on the synthesis of various metal Compounds aimed at the simulating water oxidizing complex of Photosystem II. Particular attention has been given to the Manganese Compounds not only because Manganese has been used by Nature to oxidize water but also because Manganese is cheap and environmentally friendly. In this review, we focus on Manganese Compounds as functional models of the water oxidizing complex of Photosystem II for hydrogen production via water splitting.
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Manganese Compounds as Water Oxidizing Catalysts in Artificial Photosynthesis
Artificial Photosynthesis, 2012Co-Authors: Mohammad Mahdi NajafpourAbstract:Artificial photosynthesis is an umbrella term but it could be introduced as a research field that attempts to mimic the natural process of photosynthesis and uses sunlight to oxidizing and reducing different Compounds. In this process, we could assume water as one of the Compounds that could be reduced and (or) oxidized to hydrogen and (or) oxygen, respectively. Water splitting is the general term for a chemical reaction in which water is decomposed to oxygen and hydrogen (Pace, 2005). Production of hydrogen fuel from electrolysis of water would become a practical strategy if we could find a ‘’super catalyst’’ for water oxidation reaction (Bockris, 1977). Super catalyst means a stable, low cost, efficient and environmentally friendly catalyst. The water oxidation half reaction in water splitting is overwhelmingly rate limiting and needs high over-voltage (~1V) that results the low conversion efficiencies when working at current densities required, also at this high voltage, other chemicals will be oxidized and this would be environmentally unacceptable for large-scale hydrogen production (Bockris, 1977). Thus, a significant challenge in the sustainable hydrogen economy is to design a water oxidizing catalyst.
J H V J Brabers - One of the best experts on this subject based on the ideXlab platform.
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Magnetic properties of rare earth-Manganese Compounds of the type RMnSi2
Journal of Alloys and Compounds, 1994Co-Authors: Penelope Schobinger-papamantellos, J H V J Brabers, F R De Boer, K H J BuschowAbstract:Abstract We have studied the temperature dependence of the intrinsic coercivity of the Compounds RMnSi 2 (R La, Ce, Pr, Nd) from 4.2 to 300 K. The differences in coercivity behaviour observed for these Compounds were correlated with the corresponding temperature behaviour of the magnetic structures and with the valence instability of Ce in CeMnSi 2 . Magnetic isotherms of LaMnSi 2 and CeMnSi 2 at 4.2 K were studied in field strengths up to 35 T. Neutron diffraction measurements were performed on CeMnSi 2 at 8 and 408 K. From the results of neutron diffraction and high field measurements it was concluded that Ce loses its magnetic moment at low temperatures. This is the first example of a strongly ferromagnetic compound in which Ce has an unstable valence.
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magnetic properties of rare earth Manganese Compounds of the rmn6ge6 type
Journal of Alloys and Compounds, 1993Co-Authors: J H V J Brabers, V H M Duijn, F R De Boer, K H J BuschowAbstract:Abstract We determined the magnetic properties of several Compounds of the type RMn 6 Ge 6 (R is a heavy rare-earth element). Several of these Compounds give rise to two ordering temperatures associated with antiferromagnetic ordering of the R and Mn sublattices. For GdMn 6 Sn 6 and to some extent also for TbMn 6 Sn 6 we observed magnetic behaviour which can be described as “bootstrap ferrimagnetism”: the antiferromagnetic configurations within both the R and Mn sublattices are broken simultaneously by the R-Mn intersublattice interaction, leading to ferrimagnetic alignment of the R and Mn sublattices. This bootstrap mechanism is sufficiently strong only if the intrasublattice Mn-Mn interaction is sufficiently weak. This condition is met only when the unit cell volume is sufficiently large. The interplay between intersublattice coupling and unit cell volume leads to interesting temperature dependences of the magnetization. In the magnetic isotherms the bootstrap mechanism leads to first-order phase transitions.
F R De Boer - One of the best experts on this subject based on the ideXlab platform.
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Magnetic properties of rare earth-Manganese Compounds of the type RMnSi2
Journal of Alloys and Compounds, 1994Co-Authors: Penelope Schobinger-papamantellos, J H V J Brabers, F R De Boer, K H J BuschowAbstract:Abstract We have studied the temperature dependence of the intrinsic coercivity of the Compounds RMnSi 2 (R La, Ce, Pr, Nd) from 4.2 to 300 K. The differences in coercivity behaviour observed for these Compounds were correlated with the corresponding temperature behaviour of the magnetic structures and with the valence instability of Ce in CeMnSi 2 . Magnetic isotherms of LaMnSi 2 and CeMnSi 2 at 4.2 K were studied in field strengths up to 35 T. Neutron diffraction measurements were performed on CeMnSi 2 at 8 and 408 K. From the results of neutron diffraction and high field measurements it was concluded that Ce loses its magnetic moment at low temperatures. This is the first example of a strongly ferromagnetic compound in which Ce has an unstable valence.
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magnetic properties of rare earth Manganese Compounds of the rmn6ge6 type
Journal of Alloys and Compounds, 1993Co-Authors: J H V J Brabers, V H M Duijn, F R De Boer, K H J BuschowAbstract:Abstract We determined the magnetic properties of several Compounds of the type RMn 6 Ge 6 (R is a heavy rare-earth element). Several of these Compounds give rise to two ordering temperatures associated with antiferromagnetic ordering of the R and Mn sublattices. For GdMn 6 Sn 6 and to some extent also for TbMn 6 Sn 6 we observed magnetic behaviour which can be described as “bootstrap ferrimagnetism”: the antiferromagnetic configurations within both the R and Mn sublattices are broken simultaneously by the R-Mn intersublattice interaction, leading to ferrimagnetic alignment of the R and Mn sublattices. This bootstrap mechanism is sufficiently strong only if the intrasublattice Mn-Mn interaction is sufficiently weak. This condition is met only when the unit cell volume is sufficiently large. The interplay between intersublattice coupling and unit cell volume leads to interesting temperature dependences of the magnetization. In the magnetic isotherms the bootstrap mechanism leads to first-order phase transitions.