Graphene Supermaterial Goes Superpermeable: Can Be Used to Distill Alcohol

Dr Nair with the membrane. (Credit: Image courtesy of Manchester University)

Wonder material graphene has revealed another of its extraordinary properties -- University of Manchester researchers have found that it is superpermeable with respect to water.

Graphene is one of the wonders of the science world, with the potential to create foldaway mobile phones, wallpaper-thin lighting panels and the next generation of aircraft. The new finding at the University of Manchester gives graphene's potential a most surprising dimension -- graphene can also be used for distilling alcohol.

In a report published in Science, a team led by Professor Sir Andre Geim shows that graphene-based membranes are impermeable to all gases and liquids (vacuum-tight). However, water evaporates through them as quickly as if the membranes were not there at all.

This newly-found property can now be added to the already long list of superlatives describing graphene. It is the thinnest known material in the universe and the strongest ever measured. It conducts electricity and heat better than any other material. It is the stiffest one too and, at the same time, it is the most ductile. Demonstrating its remarkable properties won University of Manchester academics the Nobel Prize in Physics in 2010.

Now the University of Manchester scientists have studied membranes from a chemical derivative of graphene called graphene oxide. Graphene oxide is the same graphene sheet but it is randomly covered with other molecules such as hydroxyl groups OH-. Graphene oxide sheets stack on top of each other and form a laminate.

The researchers prepared such laminates that were hundreds times thinner than a human hair but remained strong, flexible and were easy to handle.

When a metal container was sealed with such a film, even the most sensitive equipment was unable to detect air or any other gas, including helium, to leak through.

It came as a complete surprise that, when the researchers tried the same with ordinary water, they found that it evaporates without noticing the graphene seal. Water molecules diffused through the graphene-oxide membranes with such a great speed that the evaporation rate was the same independently whether the container was sealed or completely open.

Dr Rahul Nair, who was leading the experimental work, offers the following explanation: "Graphene oxide sheets arrange in such a way that between them there is room for exactly one layer of water molecules. They arrange themselves in one molecule thick sheets of ice which slide along the graphene surface with practically no friction.

"If another atom or molecule tries the same trick, it finds that graphene capillaries either shrink in low humidity or get clogged with water molecules."

"Helium gas is hard to stop. It slowly leaks even through a millimetre -thick window glass but our ultra-thin films completely block it. At the same time, water evaporates through them unimpeded. Materials cannot behave any stranger," comments Professor Geim. "You cannot help wondering what else graphene has in store for us."

"This unique property can be used in situations where one needs to remove water from a mixture or a container, while keeping in all the other ingredients," says Dr Irina Grigorieva who also participated in the research.

"Just for a laugh, we sealed a bottle of vodka with our membranes and found that the distilled solution became stronger and stronger with time. Neither of us drinks vodka but it was great fun to do the experiment," adds Dr Nair.

The Manchester researchers report this experiment in theirScience paper, too, but they say they do not envisage use of graphene in distilleries, nor offer any immediate ideas for applications.

However, Professor Geim adds 'The properties are so unusual that it is hard to imagine that they cannot find some use in the design of filtration, separation or barrier membranes and for selective removal of water'.

Story Source:

The above story is reprinted from materials provided byManchester University, via AlphaGalileo.

Note: Materials may be edited for content and length. For further information, please contact the source cited above.

---

Journal Reference:

1. R. R. Nair, H. A. Wu, P. N. Jayaram, I. V. Grigorieva, A. K. Geim. Unimpeded Permeation of Water Through Helium-Leak-Tight Graphene-Based Membranes.Science, 2012; 335 (6067): 442 DOI:10.1126/science.1211694

Chiral metal surfaces may help to manufacture pharmaceuticals; Novel approach could be used in pharmaceutical drug synthesis

ScienceDaily (Oct. 26, 2011) — New research shows how metal surfaces that lack mirror symmetry could provide a novel approach towards manufacturing pharmaceuticals.

These 'intrinsically chiral' metal surfaces offer potential new ways to control chiral chemistry, pointing to the intriguing possibility of using heterogeneous catalysis in drug synthesis. Such surfaces could also become the basis of new biosensor technologies.

A chiral object, such as your hand, is one that cannot be superposed on its mirror image. Chirality is fundamental in biochemistry. The building blocks of life -- amino acids and sugars -- are chiral molecules: their molecular structures can exist in either "left-handed" or "right-handed" forms (or "enantiomers").

A living organism may respond differently to the two enantiomers of a chiral substance. This is crucially important in the case of pharmaceutical drugs, where the therapeutic effect is often tied strongly to just one enantiomer of the drug molecule. Controlling chirality is therefore vital in pharmaceutical synthesis.

Research into controlling chiral synthesis focuses mainly on using homogeneous catalysts, where the catalyst is in the same phase as the reactants and products, such as a liquid added to a liquid-phase reaction. However, this poses significant practical challenges in recovering the valuable catalyst material from the mixture. To avoid this problem, an attractive alternative would be heterogeneous catalysis over a solid surface -- the type of catalysis used in catalytic converters in car exhaust systems, as well as in industrial Haber-Bosch synthesis of ammonia and Fischer-Tropsch synthesis of synthetic fuel, for example. The question then is how to achieve enantiomer-specific effects at a surface.

To help answer this question, scientists at the University of Cambridge have been probing the spontaneous self-organization of a simple chiral amino acid, alanine, into regular molecular arrays on copper single-crystal surfaces. Thanks to a powerful scanning tunnelling microscope, capable of resolving individual atoms and molecules, their work is revealing the various manifestations of chirality that occur, giving important clues to how they arise, and how they might be controlled and exploited.

Dr Stephen Driver, of the Department of Chemistry at the University of Cambridge, who led the experimental work, said: "We set out to investigate two distinct scenarios. In one scenario, the surface is non-chiral, so any chirality that we see can only arise from the chirality of the alanine molecule. In the other scenario, we move to a surface that is intrinsically chiral. Now the question becomes: do the two enantiomers of alanine behave differently on this chiral surface?"

On the non-chiral surface, the researchers found that alanine can self-organise into either of two patterns. In one of these, the self-organisation is driven by hydrogen bonding between the molecules, while the chiral centre has no discernable impact on the regular array. In the other structure, a network of long-range chiral boundaries punctuates the array, and the boundary chirality switches with molecular chirality.

Driver explained: "The implication is that the chiral centre is having a direct influence on the packing of two alanine neighbours at the boundary, and that the chirality of this pair propagates to the next pair and the next and so on, so that the chiral boundary is built up over a long range."

The chiral surface is created simply by choosing a surface orientation that lies away from any of the bulk mirror symmetry planes of the metal crystal. When the researchers added alanine, they found that the surface changes its local orientation, forming nanometre-scale facets. The two enantiomers of alanine self-organise into different chiral patterns: a strong, enantiomer-specific structural effect. This "proof of principle" could potentially be exploited in chiral recognition, in chiral synthesis (forming a chiral product from non-chiral reactants), and in chiral separations.

Driver added: "It looks like alanine can shape a comfortable, chiral bonding site for itself. The copper surface has the flexibility to adapt itself to the shape of the alanine molecule, and this shape is different for the two different molecular enantiomers."

The results imply that certain surface orientations will form stable, ordered structures with one molecular enantiomer but not the other: exactly the right conditions to promote chiral chemical effects.

Professor Sir David King, former Chief Scientific Advisor to the UK Government and current Director of the Smith School of Enterprise and the Environment at Oxford, brought together the team carrying out this research. "These results are very exciting," said King. "Tailoring the right surface to the right molecule should lead to strong enantiospecific effects. We see a real basis here for a breakthrough technology in the pharmaceuticals sector. It's something that pharma companies should be taking a close interest in."

The Cambridge team's findings are published in Topics in Catalysis.

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The above story is reprinted from materials provided by University of Cambridge. The original story is licensed under a Creative Commons license.

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Journal Reference:

Marian L. Clegg, Leonardo Morales de la Garza, Sofia Karakatsani, David A. King, Stephen M. Driver. Chirality in Amino Acid Overlayers on Cu Surfaces. Topics in Catalysis, 2011; DOI: 10.1007/s11244-011-9758-y

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View the original article here

Ceramics researchers shed light on metal embrittlement

ScienceDaily (Sep. 26, 2011) — Why does a solid metal that is engineered for ductility become brittle, often suddenly and with dramatic consequences, in the presence of certain liquid metal impurities? The phenomenon, known as liquid metal embrittlement, or LME, has baffled metallurgists for a century.

Now, a team of ceramics researchers has shed light on LME by obtaining atomic-scale images of unprecedented resolution of the grain boundaries, or internal interfaces, where LME occurs.

In doing so, says Martin Harmer, professor of materials science and engineering at Lehigh University, the researchers have achieved the first direct observation in a metal system of a bilayer grain boundary phase transition.

The study suggests that interior interfaces can undergo transitions similar to the solid-to-liquid and liquid-to-gas phase transitions that occur in larger, "bulk" materials.

It also paves the way for scientists to prevent LME by strengthening the chemical bonds of the materials present at grain boundaries.

"This is a very exciting discovery," says Harmer, who directs Lehigh's Center for Advanced Materials and Nanotechnology. "It gives us a much clearer understanding of the atomic mechanism of LME and it promises to improve our ability to control and fine-tune the properties of metals and other materials during fabrication."

Harmer and his colleagues reported their findings Sept. 23 in Science magazine.

Their 18-month study was funded by the U.S. Navy. The group will continue its work, with a focus on rectifying LME-related problems in metals, with help from a five-year, $7.5 million grant through the Department of Defense's Multidisciplinary University Research Initiative program. That project involves researchers from Lehigh, Carnegie-Mellon, Clemson, Illinois and Kutztown universities.

The common ground of ceramics and metals

Many of the consequences of LME affect everyday life, says Harmer.

A steel highway signpost can crack because LME weakened it by the molten zinc alloy applied to the steel during fabrication. Mercury and gallium, both liquid at room temperature, cause normally corrosion-resistant aluminum to become brittle. And concerns over LME make nuclear power plant operators hesitate to switch from water to liquid metal coolant, whose higher boiling point and ability to absorb radiation give it superior and more reliable cooling properties.

Harmer, who has spent 30 years studying ceramics, became interested in LME after he and his students in 2006 identified six grain-boundary "complexions," each with a distinct rate of grain growth, in the ceramic alumina.

He described complexions, and their influence on material properties, in an article titled "The Phase Behavior of Interfaces," which was published April 8 in the Perspective section of Science.

The discovery of grain-boundary complexions in ceramics, Harmer says, prompted him to seek insight into the embrittlement of metals.

"Our ideas on complexions can be tested more rigorously with metals than with ceramics because metals are simpler systems than ceramics," he says.

Harmer's group examined a nickel-bismuth alloy using Lehigh's JEOL 2200 FS aberration-corrected scanning transmission electron microscope (STEM), which has unparalleled imaging capabilities. The group employed a technique called high-angle annular dark-field imaging (HAADF), which focuses a beam of electrons only 1 angstrom (0.1 nm) wide on a sample.

Previous studies had revealed the existence of four interfacial phases at grain boundaries (GB) in metals -- a clean, or intrinsic GB, a monolayer/submonolayer, a nanometer-thick intergranular film, and a complete GB wetting film.

The aberration-corrected STEM revealed two additional GB phases -- a bilayer and a trilayer.

"A bilayer had been seen before in a ceramic system," says Harmer, "but no one had seen such examples of the bi- and trilayers in metals."

The aberration-corrected STEM pinpointed the bilayer of bismuth atoms at the grain boundary as the source of a weak atomic-scale bond in the nickel-bismuth alloy.

"The bonding is so weak that the grains come apart almost like the opening of a slippery zipper," says Harmer.

"There is a very strong bond between bismuth and nickel, so it had never been clear why the alloy is prone to embrittlement. But the bonds between bismuth atoms are weak. We are the first group to see the formation of a bismuth bilayer that weakens this material."

A comprehensive study

Harmer described his group's study as "exhaustive." The researchers examined 12 independent interfaces and took care to exclude artificial "imaging artifacts" introduced by experimental error or by technology.

They also attempted to ensure that their images represented the 3-D nature of nickel-bismuth.

"When you project a 3-D image onto a 2-D film, distortions can result. To avoid this, we imaged at different depths on the sample. By looking sequentially at these images and their structural thickness, we were able to rule out artifacts that give the illusion of a bilayer."

In contrast with previous studies, most of which looked at synthetic bi-crystals, Harmer's group examined polycrystalline nickel which resembles industrial materials.

"Real grain boundaries are typically less symmetrical and have higher energy than synthetic bi-crystals," says Harmer, "and they show other differences as well."

The group plans next to attempt to experiment with the chemistry of nickel-bismuth GBs to produce a more ductile behavior.

"Perhaps combining the bismuth with other elements that bond at the interface will prove effective," says Harmer.

A new aberration-corrected microscope that Lehigh is acquiring in early 2012 -- the JEOL ARM2200F STEM -- will improve the group's ability to do atomic-scale chemical analysis of grain boundaries, says Harmer.

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Story Source:

The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by Lehigh University, via EurekAlert!, a service of AAAS.

Journal References:

J. Luo, H. Cheng, K. M. Asl, C. J. Kiely, M. P. Harmer. The Role of a Bilayer Interfacial Phase on Liquid Metal Embrittlement. Science, 2011; 333 (6050): 1730 DOI: 10.1126/science.1208774M. P. Harmer. The Phase Behavior of Interfaces. Science, 2011; 332 (6026): 182 DOI: 10.1126/science.1204204

Note: If no author is given, the source is cited instead.

Disclaimer: Views expressed in this article do not necessarily reflect those of ScienceDaily or its staff.

View the original article here

New metal hydride clusters provide insights into hydrogen storage

ScienceDaily (Sep. 23, 2011) — A study published by researchers at the RIKEN Advanced Science Institute (ASI) has shed first-ever light on a class of heterometallic molecular structures whose unique features point the way to breakthroughs in the development of lightweight fuel cell technology. The structures contain a previously-unexplored combination of rare-earth and d-transition metals ideally suited to the compact storage of hydrogen.

The most abundant element in the universe, hydrogen holds great promise as a source of clean, renewable energy, producing nothing but water as a byproduct and thus avoiding the environmental dangers associated with existing mainstream energy sources. Broad adoption of hydrogen, however, has stalled because in its natural gaseous state, the element simply takes up too much space to store and transport efficiently.

One way to solve this problem is to use metal hydrides, metallic compounds that incorporate hydrogen atoms, as a storage medium for hydrogen. In this technique, the metal hydrides bind to hydrogen to produce a solid one thousand times or more smaller than the original hydrogen gas. The hydrogen can then later be released from the solid by heating it to a given temperature.

The new heterometallic hydride clusters synthesized by the RIKEN researchers use rare-earth and d-transition metals as building blocks and exploit the advantages of both. Rare earth metal hydrides remove one major obstacle by enabling analysis using X-ray diffraction, a technique which is infeasible for most other metal hydrides -- offering unique insights into underlying reaction processes involved. Rare earth metal hydrides on their own, however, do not undergo reversible hydrogen addition and release, the cornerstone of hydrogen storage. This becomes possible through the addition of a d-transition metal, in this case tungsten (W) or molybdenum (Mo).

While rare-earth / d-transition metal-type metallic hydride complexes have been studied in the past, the current research is the first to explore complexes with multiple rare earth atoms of the form Ln4MHn and with well-defined structures (Ln = a rare-earth metal such as yttrium, M = a d-transition metal, either tungsten or molybdenum, and H = hydrogen). In a paper in Nature Chemistry, the researchers show that these complexes exhibit unique reactivity properties, pointing the way to new hydrogen storage techniques and promising environmentally-friendly solutions to today's pressing energy needs.

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Story Source:

The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by RIKEN.

Journal Reference:

Takanori Shima, Yi Luo, Timothy Stewart, Robert Bau, Garry J. McIntyre, Sax A. Mason, Zhaomin Hou. Molecular heterometallic hydride clusters composed of rare-earth and d-transition metals. Nature Chemistry, 2011; DOI: 10.1038/NCHEM.1147

Note: If no author is given, the source is cited instead.

Disclaimer: Views expressed in this article do not necessarily reflect those of ScienceDaily or its staff.

View the original article here

Hydrogen released to fuel cell more quickly when stored in metal nanoparticles

ScienceDaily (Oct. 1, 2011) — Researchers from TU Delft and VU University Amsterdam in the Netherlands have demonstrated that the size of a metal alloy nanoparticle influences the speed with which hydrogen gas is released when stored in a metal hydride. The smaller the size of the nanoparticle, the greater the speed at which the hydrogen gas makes its way to the fuel cell.

The researchers publish their findings in the October issue of the scientific journal Advanced Energy Materials.

Hydrogen heaven

On 27 September Dutch Minister of Infrastructure and the Environment, Ms Schultz van Haegen, announced she will earmark 5 million Euros to stimulate hydrogen transport in the Netherlands. According to the Minister the Netherlands and neighbouring countries have all it takes to become a 'hydrogen heaven'. In July 2011, the German car manufacturer Daimler announced its intention to build twenty new hydrogen fuelling stations along Germany's motorways. Hydrogen is back on the agenda. Hydrogen gas is currently stored in a vehicle fuel tank at 700 bar pressure. Fuelling stations thus require high-pressure pumps to fill these tanks and these systems consume a lot of energy.

Hydrogen storage

There are thus good reasons for finding alternative hydrogen storage techniques. Hydrogen can be absorbed in high densities in metals such as magnesium, without the need for high pressure. However, the disadvantage is that releasing the hydrogen again is a very difficult and very slow process. One way of speeding up the release of the hydrogen is to use magnesium nanoparticles that are fixed in a matrix to prevent them from aggregating.

Nanoparticles in a matrix

Professor of Materials for Energy Conversion and Storage, Bernard Dam, and his colleagues at TU Delft and VU University Amsterdam have demonstrated experimentally that the interaction between the nanoparticles and the matrix can cause the hydrogen gas to be released faster. Using models consisting of thin layers of magnesium and titanium, they show how the pressure of the hydrogen being released from the magnesium increases as the layers become thinner. This means that it indeed makes sense to store hydrogen in nanoparticles in a matrix. The choice of matrix determines to what extent the hydrogen desorption pressure increases. The researchers published their findings in the October 2011 edition of the scientific journal Advanced Energy Materials.

Efficient and affordable hydrogen storage techniques can play an important role in the large-scale adoption of hydrogen fuel cells. Bernard Dam foresees the development of hybrid vehicles that use batteries for short distances but switch to hydrogen for long distances: 'Your electric motor will be powered by batteries inside the city, and by hydrogen when you go further afield.'

The research was funded by the ACTS Sustainable Hydrogen Program of the Netherlands Organisation for Scientific Research.

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Story Source:

The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by Delft University of Technology.

Journal Reference:

Lennard P.A. Mooij, Andrea Baldi, Christiaan Boelsma, Kun Shen, Marnix Wagemaker, Yevheniy Pivak, Herman Schreuders, Ronald Griessen, Bernard Dam. Interface Energy Controlled Thermodynamics of Nanoscale Metal Hydrides. Advanced Energy Materials, Volume 1, issue 5, pages 754-758, October 2011.

Note: If no author is given, the source is cited instead.

Disclaimer: Views expressed in this article do not necessarily reflect those of ScienceDaily or its staff.

View the original article here

Ceramics researchers shed light on metal embrittlement

ScienceDaily (Sep. 26, 2011) — Why does a solid metal that is engineered for ductility become brittle, often suddenly and with dramatic consequences, in the presence of certain liquid metal impurities? The phenomenon, known as liquid metal embrittlement, or LME, has baffled metallurgists for a century.

Now, a team of ceramics researchers has shed light on LME by obtaining atomic-scale images of unprecedented resolution of the grain boundaries, or internal interfaces, where LME occurs.

In doing so, says Martin Harmer, professor of materials science and engineering at Lehigh University, the researchers have achieved the first direct observation in a metal system of a bilayer grain boundary phase transition.

The study suggests that interior interfaces can undergo transitions similar to the solid-to-liquid and liquid-to-gas phase transitions that occur in larger, "bulk" materials.

It also paves the way for scientists to prevent LME by strengthening the chemical bonds of the materials present at grain boundaries.

"This is a very exciting discovery," says Harmer, who directs Lehigh's Center for Advanced Materials and Nanotechnology. "It gives us a much clearer understanding of the atomic mechanism of LME and it promises to improve our ability to control and fine-tune the properties of metals and other materials during fabrication."

Harmer and his colleagues reported their findings Sept. 23 in Science magazine.

Their 18-month study was funded by the U.S. Navy. The group will continue its work, with a focus on rectifying LME-related problems in metals, with help from a five-year, $7.5 million grant through the Department of Defense's Multidisciplinary University Research Initiative program. That project involves researchers from Lehigh, Carnegie-Mellon, Clemson, Illinois and Kutztown universities.

The common ground of ceramics and metals

Many of the consequences of LME affect everyday life, says Harmer.

A steel highway signpost can crack because LME weakened it by the molten zinc alloy applied to the steel during fabrication. Mercury and gallium, both liquid at room temperature, cause normally corrosion-resistant aluminum to become brittle. And concerns over LME make nuclear power plant operators hesitate to switch from water to liquid metal coolant, whose higher boiling point and ability to absorb radiation give it superior and more reliable cooling properties.

Harmer, who has spent 30 years studying ceramics, became interested in LME after he and his students in 2006 identified six grain-boundary "complexions," each with a distinct rate of grain growth, in the ceramic alumina.

He described complexions, and their influence on material properties, in an article titled "The Phase Behavior of Interfaces," which was published April 8 in the Perspective section of Science.

The discovery of grain-boundary complexions in ceramics, Harmer says, prompted him to seek insight into the embrittlement of metals.

"Our ideas on complexions can be tested more rigorously with metals than with ceramics because metals are simpler systems than ceramics," he says.

Harmer's group examined a nickel-bismuth alloy using Lehigh's JEOL 2200 FS aberration-corrected scanning transmission electron microscope (STEM), which has unparalleled imaging capabilities. The group employed a technique called high-angle annular dark-field imaging (HAADF), which focuses a beam of electrons only 1 angstrom (0.1 nm) wide on a sample.

Previous studies had revealed the existence of four interfacial phases at grain boundaries (GB) in metals -- a clean, or intrinsic GB, a monolayer/submonolayer, a nanometer-thick intergranular film, and a complete GB wetting film.

The aberration-corrected STEM revealed two additional GB phases -- a bilayer and a trilayer.

"A bilayer had been seen before in a ceramic system," says Harmer, "but no one had seen such examples of the bi- and trilayers in metals."

The aberration-corrected STEM pinpointed the bilayer of bismuth atoms at the grain boundary as the source of a weak atomic-scale bond in the nickel-bismuth alloy.

"The bonding is so weak that the grains come apart almost like the opening of a slippery zipper," says Harmer.

"There is a very strong bond between bismuth and nickel, so it had never been clear why the alloy is prone to embrittlement. But the bonds between bismuth atoms are weak. We are the first group to see the formation of a bismuth bilayer that weakens this material."

A comprehensive study

Harmer described his group's study as "exhaustive." The researchers examined 12 independent interfaces and took care to exclude artificial "imaging artifacts" introduced by experimental error or by technology.

They also attempted to ensure that their images represented the 3-D nature of nickel-bismuth.

"When you project a 3-D image onto a 2-D film, distortions can result. To avoid this, we imaged at different depths on the sample. By looking sequentially at these images and their structural thickness, we were able to rule out artifacts that give the illusion of a bilayer."

In contrast with previous studies, most of which looked at synthetic bi-crystals, Harmer's group examined polycrystalline nickel which resembles industrial materials.

"Real grain boundaries are typically less symmetrical and have higher energy than synthetic bi-crystals," says Harmer, "and they show other differences as well."

The group plans next to attempt to experiment with the chemistry of nickel-bismuth GBs to produce a more ductile behavior.

"Perhaps combining the bismuth with other elements that bond at the interface will prove effective," says Harmer.

A new aberration-corrected microscope that Lehigh is acquiring in early 2012 -- the JEOL ARM2200F STEM -- will improve the group's ability to do atomic-scale chemical analysis of grain boundaries, says Harmer.

Recommend this story on Facebook, Twitter,
and Google +1:

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Story Source:

The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by Lehigh University, via EurekAlert!, a service of AAAS.

Journal References:

J. Luo, H. Cheng, K. M. Asl, C. J. Kiely, M. P. Harmer. The Role of a Bilayer Interfacial Phase on Liquid Metal Embrittlement. Science, 2011; 333 (6050): 1730 DOI: 10.1126/science.1208774M. P. Harmer. The Phase Behavior of Interfaces. Science, 2011; 332 (6026): 182 DOI: 10.1126/science.1204204

Note: If no author is given, the source is cited instead.

Disclaimer: Views expressed in this article do not necessarily reflect those of ScienceDaily or its staff.

View the original article here

New metal hydride clusters provide insights into hydrogen storage

ScienceDaily (Sep. 23, 2011) — A study published by researchers at the RIKEN Advanced Science Institute (ASI) has shed first-ever light on a class of heterometallic molecular structures whose unique features point the way to breakthroughs in the development of lightweight fuel cell technology. The structures contain a previously-unexplored combination of rare-earth and d-transition metals ideally suited to the compact storage of hydrogen.

The most abundant element in the universe, hydrogen holds great promise as a source of clean, renewable energy, producing nothing but water as a byproduct and thus avoiding the environmental dangers associated with existing mainstream energy sources. Broad adoption of hydrogen, however, has stalled because in its natural gaseous state, the element simply takes up too much space to store and transport efficiently.

One way to solve this problem is to use metal hydrides, metallic compounds that incorporate hydrogen atoms, as a storage medium for hydrogen. In this technique, the metal hydrides bind to hydrogen to produce a solid one thousand times or more smaller than the original hydrogen gas. The hydrogen can then later be released from the solid by heating it to a given temperature.

The new heterometallic hydride clusters synthesized by the RIKEN researchers use rare-earth and d-transition metals as building blocks and exploit the advantages of both. Rare earth metal hydrides remove one major obstacle by enabling analysis using X-ray diffraction, a technique which is infeasible for most other metal hydrides -- offering unique insights into underlying reaction processes involved. Rare earth metal hydrides on their own, however, do not undergo reversible hydrogen addition and release, the cornerstone of hydrogen storage. This becomes possible through the addition of a d-transition metal, in this case tungsten (W) or molybdenum (Mo).

While rare-earth / d-transition metal-type metallic hydride complexes have been studied in the past, the current research is the first to explore complexes with multiple rare earth atoms of the form Ln4MHn and with well-defined structures (Ln = a rare-earth metal such as yttrium, M = a d-transition metal, either tungsten or molybdenum, and H = hydrogen). In a paper in Nature Chemistry, the researchers show that these complexes exhibit unique reactivity properties, pointing the way to new hydrogen storage techniques and promising environmentally-friendly solutions to today's pressing energy needs.

Recommend this story on Facebook, Twitter,
and Google +1:

Other bookmarking and sharing tools:

Story Source:

The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by RIKEN.

Journal Reference:

Takanori Shima, Yi Luo, Timothy Stewart, Robert Bau, Garry J. McIntyre, Sax A. Mason, Zhaomin Hou. Molecular heterometallic hydride clusters composed of rare-earth and d-transition metals. Nature Chemistry, 2011; DOI: 10.1038/NCHEM.1147

Note: If no author is given, the source is cited instead.

Disclaimer: Views expressed in this article do not necessarily reflect those of ScienceDaily or its staff.

View the original article here

Hydrogen released to fuel cell more quickly when stored in metal nanoparticles

ScienceDaily (Oct. 1, 2011) — Researchers from TU Delft and VU University Amsterdam in the Netherlands have demonstrated that the size of a metal alloy nanoparticle influences the speed with which hydrogen gas is released when stored in a metal hydride. The smaller the size of the nanoparticle, the greater the speed at which the hydrogen gas makes its way to the fuel cell.

The researchers publish their findings in the October issue of the scientific journal Advanced Energy Materials.

Hydrogen heaven

On 27 September Dutch Minister of Infrastructure and the Environment, Ms Schultz van Haegen, announced she will earmark 5 million Euros to stimulate hydrogen transport in the Netherlands. According to the Minister the Netherlands and neighbouring countries have all it takes to become a 'hydrogen heaven'. In July 2011, the German car manufacturer Daimler announced its intention to build twenty new hydrogen fuelling stations along Germany's motorways. Hydrogen is back on the agenda. Hydrogen gas is currently stored in a vehicle fuel tank at 700 bar pressure. Fuelling stations thus require high-pressure pumps to fill these tanks and these systems consume a lot of energy.

Hydrogen storage

There are thus good reasons for finding alternative hydrogen storage techniques. Hydrogen can be absorbed in high densities in metals such as magnesium, without the need for high pressure. However, the disadvantage is that releasing the hydrogen again is a very difficult and very slow process. One way of speeding up the release of the hydrogen is to use magnesium nanoparticles that are fixed in a matrix to prevent them from aggregating.

Nanoparticles in a matrix

Professor of Materials for Energy Conversion and Storage, Bernard Dam, and his colleagues at TU Delft and VU University Amsterdam have demonstrated experimentally that the interaction between the nanoparticles and the matrix can cause the hydrogen gas to be released faster. Using models consisting of thin layers of magnesium and titanium, they show how the pressure of the hydrogen being released from the magnesium increases as the layers become thinner. This means that it indeed makes sense to store hydrogen in nanoparticles in a matrix. The choice of matrix determines to what extent the hydrogen desorption pressure increases. The researchers published their findings in the October 2011 edition of the scientific journal Advanced Energy Materials.

Efficient and affordable hydrogen storage techniques can play an important role in the large-scale adoption of hydrogen fuel cells. Bernard Dam foresees the development of hybrid vehicles that use batteries for short distances but switch to hydrogen for long distances: 'Your electric motor will be powered by batteries inside the city, and by hydrogen when you go further afield.'

The research was funded by the ACTS Sustainable Hydrogen Program of the Netherlands Organisation for Scientific Research.

Recommend this story on Facebook, Twitter,
and Google +1:

Other bookmarking and sharing tools:

Story Source:

The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by Delft University of Technology.

Journal Reference:

Lennard P.A. Mooij, Andrea Baldi, Christiaan Boelsma, Kun Shen, Marnix Wagemaker, Yevheniy Pivak, Herman Schreuders, Ronald Griessen, Bernard Dam. Interface Energy Controlled Thermodynamics of Nanoscale Metal Hydrides. Advanced Energy Materials, Volume 1, issue 5, pages 754-758, October 2011.

Note: If no author is given, the source is cited instead.

Disclaimer: Views expressed in this article do not necessarily reflect those of ScienceDaily or its staff.

View the original article here