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

Nov 01, 2011

Hydrogen offers great promise as a renewable energy source. It's staggeringly plentiful (the most abundant element in the Universe) and environmentally friendly (used in a fuel cell, it gives off only water). Unfortunately, storing and transporting hydrogen for personal use is a significant engineering challenge.

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). , 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 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 , 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 ) 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 .

"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 into a noble-metal like catalyst for low-temperature molecular activation" –was published online in the journal Nature Materials on September 25.

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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

5 /5 (5 votes)

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User comments : 8

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Doug_Huffman
4 / 5 (1) Nov 01, 2011
There are more electrons than hydrogen that is no more a 'fuel' than is electricity.
rawa1
1 / 5 (3) Nov 01, 2011
The cold fusion would make all these material hungry energetic solutions unnecessary (and their research and researchers as well)..
dschlink
5 / 5 (2) Nov 01, 2011
Hydrogen is not a fuel. It must be manufactured and even the most optimistic calculations place the energy return under 20%. What hydrogen is is a very inefficient battery.
holoman
2 / 5 (1) Nov 01, 2011
Anyone who has followed the Space Shuttle knows hydrogen offers
a high energy clean green avenue for future energy.
Scottingham
not rated yet Nov 02, 2011
holoman, H2 isn't exactly high energy, and it's only clean if the power used to produce it is clean. Right now, most of it comes from natural gas...not clean. In the future it could come from dedicated fission cores....clean(99.999% of the time).
antialias_physorg
not rated yet Nov 02, 2011
Hydrogen is not a fuel. It must be manufactured and even the most optimistic calculations place the energy return under 20%.

Not quite. Best turnaround for hydrogen (calculating production, compression for storage, fuel cell efficiency, motor efficiency) is at best about 43%.

This is still better than in cars at their best (gasoline: 25-30%, diesel: 40% - not counting inefficiency due to having to drill for it, produce, refine and transport)

Battery powered cars (including motor efficiency) are at about 72% but this excludes any efficiency losses in making the electricity or transmission losses.
kaasinees
not rated yet Nov 02, 2011
Hydrogen is not a fuel. It must be manufactured and even the most optimistic calculations place the energy return under 20%.

Not quite. Best turnaround for hydrogen (calculating production, compression for storage, fuel cell efficiency, motor efficiency) is at best about 43%.

This is still better than in cars at their best (gasoline: 25-30%, diesel: 40% - not counting inefficiency due to having to drill for it, produce, refine and transport)

Battery powered cars (including motor efficiency) are at about 72% but this excludes any efficiency losses in making the electricity or transmission losses.

There is a difference in burning efficiency, refining efficiency and mining efficiency.
antialias_physorg
not rated yet Nov 02, 2011
The entire cycle must be taken into account: From production to consumption.

For fossil fuels the "production" is free (the energy has already been stored in there by the sun). Mining and refinement are not. Neither are transport which would be over larger distances than for hydrogen which can be producd more local to the end user on average. Then comes combustion efficiency.

For batteries it's the entire chain from production via transmission to storage, release, and usage. (Using alternative energy sources the production is also 'free' as no fossil energy carrier is used)

For hydrogen it's creation, compression/storage, (transport - depending on creation type), and usage (fuel cell plus motor in this case) with the same 'free' production given alternative power sources.