How to make new hydrogen

Scientists at Penn State University and Virginia Commonwealth University have discovered a way to produce hydrogen by exposing aluminum clusters to water. These findings are important because they demonstrate that the geometry of the aluminum clusters, not just their electronic properties, controls the distance of the exposed active part of the cluster. The distance of the exposed part of the cluster plays an important role in influencing the reaction of the cluster to water.

The team's findings are published in the journal Science on January 23, 2009.
A. Welford Castleman Jr., Professor at Penn State University's Department of Chemistry and Physics, said: 'Our previous study shows that electronic properties control everything in aluminum clusters, but new research shows the arrangement of atoms at the center of the cluster allowing them to divide water. This knowledge can allow us to design new nanoscale catalysts by changing the arrangement of atoms in a cluster. These results may open up a new field of research, not only related to the division of water but also the breakdown of other molecules' links .

The research team, including Penn State graduate students Patrick Roach and Hunter Woodward, and physics professor Siv Khanna and senior researcher after Dr. Arthur Rever of Virginia Commonwealth University, studied the reaction of water to individual aluminum assemblies by combining them under controlled conditions in a specially designed flow reactor. They found that a water molecule would bind between two aluminum positions in a cluster, when a position acts as a Lewis acid, the positively charged center receives an electron, and the other acts as a Lewis base, negatively charged center gives away an electron. Lewis acid aluminum binds to oxygen in water and Lewis base aluminum separates hydrogen atoms. If this process occurs a second time with two other aluminum positions and a water molecule, the two hydrogen atoms are separated and they can combine to form hydrogen gas (H2).

The image shows the aluminum cluster reacting with water to produce hydrogen. The image below shows a water molecule (an oxygen atom (red) and two hydrogen atoms (silver) that are detached on the surface of the aluminum cluster. The blue area is the Lewis acid positions, and the orange zone is the Lewis base position. The image on the upper right shows many water molecules associated with the active position of an aluminum cluster. The image on the upper left shows the release of hydrogen (two silver spheres surround an orange halo). (Photo: AC Reber, VCU / Penn State)

The team found that aluminum clusters react differently when exposed to water, depending on the size and geometry of the cluster. Three aluminum clusters produce hydrogen from water at room temperature. Khana said: 'The ability to produce hydrogen at room temperature is significant because it means that we don't have to use heat or energy to stimulate the reaction. Traditional techniques for generating hydrogen from water often require a lot of energy. But our method allows creating hydrogen without providing heat, connecting to a battery, or transmitting more electricity. When aluminum clusters are synthesized, they can produce hydrogen, depending on their needs. '

Khanna hopes the team's findings will open a new page in studying how aluminum clusters can be used and how the conditions for releasing hydrogen can be controlled. He said: 'It seems that we can have new methods to separate the hydroxyl group (OH-) still attached to the aluminum clusters after they create hydrogen, so that we can reuse aluminum clusters many times.'

The team plans to continue research work with the aim of strengthening this method. The research was funded by a non-force Scientific Research Office.