Aluminum superatoms may split water

Metal clusters could create hydrogen for fuel, simulations suggest

Tiny clusters of aluminum atoms may be able to quickly extract pure hydrogen from water, a new simulation suggests. The results offer an incredibly detailed view of how the molecules react and may help scientists develop new ways to produce pure hydrogen-based fuels, researchers report in an upcoming Physical Review Letters.

SUPERATOM BREAKS WATER An aluminum superatom (silver) produces hydrogen molecules (yellow) from water, a new simulation shows. Manaschai Kunaseth and Ken-ichi Nomura/USC Collaboratory for Advanced Computing and Simulations

Many energy experts consider hydrogen an ideal fuel, because mixing it with oxygen produces nothing but energy and water. But transporting and storing pure hydrogen is a safety challenge, and current methods of producing it on an industrial scale require more energy than the resulting hydrogen fuel contains. What’s more, that energy typically comes from natural gas, coal or other fuels that produce greenhouse gases. In order to reap hydrogen’s benefits, researchers need to find ways to create, transport and store it in a safe and sustainable way.

Computational physicist Priya Vashishta of the University of Southern California in Los Angeles is working on a way to eliminate the storage problem by producing hydrogen “on the fly.” He and colleagues from USC and Kumamato University in Japan generated complex computer simulations of a glob of 17 aluminum atoms suspended in water. This group of atoms, called a superatom, takes on special attributes that might change how the aluminum reacts with water molecules.

In their simulations, Vashishta and colleagues watched the water and aluminum molecules waltz through a choreographed routine. The effect, Vashishta says, was similar to watching characters dancing in a movie as the frames flicker by. Electrons and hydrogen ions moved around before the reaction ultimately produced three hydrogen molecules, each of which contains two hydrogen atoms, all in about 3 picoseconds. “The simulation tells us how the hydrogen is produced, and we can tell you absolutely, totally and completely the process by which it is produced,” says Vashishta.

Earlier experiments by other researchers have hinted that aluminum superatoms react with single molecules of water vapor. Small molecules such as the aluminum superatom have a high ratio of surface area to volume, giving them an advantage over bulkier substrates in reaction rates, Vashishta says.

Some regions of the superatom were hungry for electrons, while other regions wanted to give electrons away, the researchers found. As these sites began interacting with the surrounding water molecules, hydrogen atoms swiftly jumped from one oxygen partner to another, ultimately ending up on the aluminum superatom. After another series of complicated hydrogen bond switching events, a hydrogen atom then left the aluminum to join another hydrogen atom. The two hydrogen singletons were produced strategically close to one another, easing their ability to find each other and form a stable two-hydrogen molecule. Their closeness is “quite remarkable,” says Vashishta.

The results provide a more complete view of how tiny aluminum particles can catalyze hydrogen production. But these aluminum superatoms may not be a viable way to create energy, comments alternative-energy researcher Jerry Woodall of Purdue University in West Lafayette, Ind. “This is interesting science, but it’ll probably not see the realm of practicality in my lifetime,” says Woodall, who has worked on large-scale aluminum catalysts for hydrogen production.

Laura Sanders is the neuroscience writer. She holds a Ph.D. in molecular biology from the University of Southern California.

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