Aluminum alloy overcomes obstacles on the path to making hydrogen a practical fuel source

Now, a team of researchers from the University of Texas at Dallas and Washington State University in Pullman, Wash., has made the counterintuitive discovery that aluminum, with a minor modification, is able to both break down and capture individual hydrogen atoms, potentially leading to a robust and affordable fuel storage system.

In nature, when two atoms of hydrogen meet they combine to form a very stable molecule (H2). Molecular hydrogen, however, has to be stored under great pressure and at very low temperatures, which is impractical if you want to power a vehicle or provide electricity for a home. A better solution would be to find a material that, at easily maintained temperatures and pressures, could efficiently store individual hydrogen atoms and release them on demand.

The first step in this process – hydrogen activation, breaking the chemical bonds that hold two hydrogen atoms together – is typically done by exposing molecular hydrogen to a catalyst. The best catalytic materials currently available are made of so-called "noble metals" (e.g. palladium and platinum). These elements efficiently enable hydrogen activation, but their scarcity makes them prohibitively expensive for widespread use.

In the quest to find an equally efficient yet less-expensive alternative, lead researcher Yves J. Chabal of the University of Texas at Dallas and Santanu Chaudhuri at Washington State University have identified a potential new hydrogen activation method that has the additional advantage of being an effective hydrogen-storage medium. Their proposed system relies on aluminum, a plentiful but inert metal that under normal conditions doesn't react with molecular hydrogen.

The key to unlocking aluminum's potential, the researchers surmised, is to impregnate its surface with some other metal that would facilitate the catalytic reaction. In this case, the researchers tested titanium, which is much more plentiful than noble metals and is used only sparingly in creating the titanium-doped aluminum surface.

Under very controlled temperatures and pressures, the researchers studied the aluminum surface, particularly in the vicinity of the titanium atoms, for telltale signs that catalytic reactions were taking place. The "smoking gun" was found in the spectroscopic signature of carbon monoxide (CO), which was added to the system to help identify areas of hydrogen activity. If atomic hydrogen were present, then the wavelength of light absorbed by the carbon monoxide bound to the catalytic metal center would become shorter, signaling that the catalyst was working.

"We've combined a novel infrared reflection absorption-based surface analysis method and first principles-based predictive modeling of catalytic efficiencies and spectral response, in which a carbon monoxide molecule is used as a probe to identify hydrogen activation on single-crystal aluminum surfaces containing catalytic dopants," says Chaudhuri.

Their studies revealed that in areas doped with titanium, the infrared signature of the CO shifted to shorter wavelengths even at very low temperatures. This "blue shift" was an indication that atomic hydrogen was being produced around some of the catalytic centers on an aluminum surface.

As part of a hydrogen storage system, an aluminum-supported catalyst has other advantages over more expensive metals. If technical advances like this can provide a pathway for aluminum to combine with hydrogen to form aluminum hydride (a stable solid with a composition ratio of a single aluminum atom to three hydrogen atoms) and store hydrogen as a high-density solid-state material, a critical step in developing a practical fuel system can be achieved.

The titanium further advances the process by helping the hydrogen bind to the aluminum to form aluminum hydride. If used as a fuel-storage device, the aluminum hydride could be made to release its store of hydrogen by simply raising its temperature.

"Although titanium may not be the best catalytic center for fully reversible aluminum hydride formation, the results prove for the first time that titanium-doped aluminum can activate hydrogen in ways that are comparable to expensive and less-abundant catalyst metals such as palladium and other near-surface alloys consisting of similar noble metals and their bimetallic analogs," Chaudhuri explains.

Irinder Chopra, the lead student in this project, will present this research at AVS' 58th International Symposium & Exhibition, held Oct. 30 – Nov. 4, 2011, in Nashville, Tenn. A paper based on this research – "Turning Aluminum into a noble-metal like catalyst for low-temperature molecular hydrogen activation" –was published online in the journal Nature Materials on September 25.

More information: The AVS 58th International Symposium & Exhibition will be held Oct. 30 – Nov. 4 at the Nashville Convention Center. Presentation SS1-TuM-4, "Turning Aluminum into a Noble-metal like Catalyst for Low Temperature Molecular Hydrogen Activation," is at 9 a.m. on Tuesday, Nov. 1.

Provided by American Institute of Physics

A substance from bacteria can lead to allergy-free sunscreen

"Unfortunately, several of the chemical UV filters used in sunscreens cause contact allergy, either of themselves or when they are exposed to sunlight. We have therefore studied a UV filter, scytonemin, that is found in certain bacteria. We have managed to produce this substance artificially in the laboratory", says Isabella Karlsson, research student in the Department of Chemistry at the University of Gothenburg.

Sunlight contains two types of UV radiation. The type known as "UVA" penetrates deeply into the skin and causes the pigment that we already have to darken. UVA, however, also causes the skin to age prematurely. The most common chemical UVA filter on the market is 4-tert-butyl-4'-methoxy dibenzoylmethane, BM-DBM, which is known to cause photocontact allergy when it reacts on the skin. Isabella Karlsson has shown that BM-DBM breaks down in UV light to form several different products. One of these, a group of substances known as "arylglyoxals", proved to be very potent contact allergens.

Isabella Karlsson also describes in her thesis studies of a relatively new UV filter, octocrylene. The popularity of octocrylene has increased a great deal since it is not broken down by sunlight, and it stabilises other substances such as, for example, BM-DBM. However, several reports of allergic reactions to octocrylene have appeared in recent years. Clinical studies and laboratory experiments have suggested that octocrylene can cause contact allergy, both of itself and when it is exposed to sunlight. Many patients who reacted by developing photocontact allergy to octocrylene developed photocontact allergy also to the drug ketoprofen.

"We tested 172 patients with suspected skin reactions to sunscreen creams and/or the drug ketoprofen in one of our studies. It turned out that 23 of these patients reacted to the UV filter octocrylene. Five of them were diagnosed with contact allergy and the other 18 with photocontact allergy."

So Isabella Karlsson is placing her hopes onto the natural product scytonemin. She has managed to produce this substance artificially, in collaboration with Chalmers University of Technology. Scytonemin is produced by certain cyanobacteria that live in habitats exposed to very strong sunlight. Scytonemin absorbs UV light and thus protects the bacteria from being damaged by the sun's radiation. More research will be required, however, before it can be added to sunscreen creams.

Provided by University of Gothenburg (news : web)

A simple compound with surprising antifreeze properties

The formation of ice crystals can have multiple, and often destructive, consequences. Cell degradation in living organisms, damage to land and roads in cold climates, ice crystals in ice creams… These are all examples of situations where it is useful to control ice growth. Many organisms and species that live in cold environments have adapted to control ice growth. Their resistance to low temperatures is based on the presence of antifreeze proteins, all of which are made up of very long organic chains with amphiphilic structures (partly hydrophilic, partly hydrophobic). How do these proteins interact with ice crystals? Researchers are trying to identify the mechanism enabling antifreeze proteins to identify these crystals, but the phenomenon is still not fully understood. In addition, since these proteins are extremely costly to extract, the preferred solution is to create synthetic equivalents inspired by natural structures. All proteins currently known for their “antifreeze” properties are macromolecules (like glycoproteins, polysaccharides, etc.).

A team led by Sylvain Deville, CNRS researcher at the LSFC (Laboratoire de Synthese et Fonctionnalisation des Céramiques, Synthesis and Functionalization of Ceramics Laboratory, CNRS/Saint-Gobain), in collaboration with the Matériaux, Ingénierie et Sciences (Materials, Engineering and Sciences) laboratory, has discovered that zirconium acetate, a chemical compound normally used to stabilize particles in suspension, can control ice crystal growth. The compound governs the morphology of the ice crystals obtained by freezing a solution in which it is combined with water. The crystals obtained when adding zirconium acetate are very homogenous, whereas those obtained without it show no particular uniformity.

These results are quite surprising, given that zirconium acetate is a “salt,” a simple compound that is radically different from the macromolecules known for their antifreeze properties. It was not known as a substance capable of controlling ice crystal growth. Such control can be exerted in a number of ways: by reducing the speed of crystal growth (to slow their formation), by lowering the freezing point (to delay their formation), or by controlling their morphology, as in this case. Since this implies a direct interaction with the ice crystals, the researchers were surprised to find out that such radically different molecules as zirconium acetate and proteins could affect crystalline growth.

This compound offers significant advantages over existing equivalents, whether natural or synthetic. It is cheap to produce, stable, “simple” and easy to use, which bodes well for a wealth of future industrial applications. In addition, since it is totally different from all previously identified and/or developed substances with the same function, further research could lead to the development of other molecules with antifreeze properties.

This project relied on X-ray diffraction and imaging. These works were made possible by using the X-ray synchrotron (beam line ID19) at the ESRF in Grenoble, France. They are covered by two patents published on October 1, 2011.

More information: Ice shaping properties, similar to that of antifreeze proteins, of a zirconium acetate complex. Sylvain Deville, et al. PLoS ONE. 18 October 2011. doi:10.1371/journal.pone.0026474

Provided by CNRS (news : web)

Breakthrough holds promise for hydrogen's use as fuel source

“Hydrogen, which is in abundance all around us, has shown a lot of promise as an alternative fuel source in recent years,” said UT Dallas graduate student Irinder Singh Chopra. “Moreover, it’s environmentally friendly as it gives off only water after combustion.”

Chopra is part of a collaborative effort among UT Dallas, Washington State University and Brookhaven National Laboratory to find ways to store hydrogen for use as an alternative fuel.

Hydrogen has potential for use as an everyday fuel, but the problem of safely storing this highly flammable, colorless gas is a technological hurdle that has kept it from being a viable option.

“We investigated a certain class of materials called complex metal hydrides (aluminum-based hydrides) in the hope of finding cheaper and more effective means of activating hydrogen,” Chopra said.

“Our research into an aluminum-based catalyst turned out to be much more useful than just designing good storage materials,” he said. “It has also provided very encouraging results into the possible use of this system as a very cheap and effective alternative to the materials currently used for fuel cells.”

This is the first step in producing many important industrial chemicals that have so far required expensive noble-metal catalysts and thermal activation. Essentially, the process can easily break apart molecular hydrogen and capture the individual atoms, potentially leading to a robust and affordable fuel storage system or a cheap catalyst for important industrial reactions.

Chopra discovered that the key to unlocking aluminum's potential is to impregnate its surface with trace amounts of titanium that can catalyze the separation of molecular hydrogen.

“It has long been theoretically predicted that titanium-doped aluminum can be used as an effective catalyst,” Chopra said. “We discovered, however, that a specific arrangement of titanium atoms was critical and made it possible to produce atomic hydrogen on aluminum surfaces at remarkably low temperatures.”

For use as a fuel-storage device, aluminum could be made to release its store of hydrogen by raising its temperature slightly. This system presents a method for storing and releasing hydrogen at lower temperatures than what is currently available, which is critical for safe day-to-day applications.

To perform these experiments, Dr. Jean-Francois Veyan, a research scientist in Chabal’s lab, greatly assisted Chopra in the design and construction of a sophisticated ultra-high vacuum equipment.

“A critical aspect of the work was the ability to clean single crystal aluminum samples without damaging the arrangement of the surface atoms,” Veyan said. “Experience gathered from my earlier PhD work on aluminum was very important to help prepare these novel Ti-doped surfaces.”

Dr. Yves Chabal, Texas Instruments Distinguished University Chair in Nanoelectronics and head of the University’s Department of Materials Science and Engineering, who oversaw the research program, praised the team’s achievements.

“This is a good example of the kind of collaborative research that can lead to new advances in the field,” Chabal said, “and how painstaking work started five years ago can bring unexpected and exciting results.”

More information: http://www.nature. … mat3123.html

Provided by University of Texas at Dallas (news : web)