Aluminum Eases Hydrogen Generation

Exposing clusters of aluminum to water can generate hydrogen at ambient conditions without need for heat or energy,

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Exposing clusters of aluminum to water can generate hydrogen at ambient conditions without need for heat or energy, report researchers at Pennsylvania State University (PSU), University Park, Pa., and Virginia Commonwealth University (VCU), Richmond, Va.

“The ability to produce hydrogen at room temperature is significant because it means that we did not use any heat or energy to trigger the reaction,” notes Shiv Khanna, a professor of physics at VCU. “Traditional techniques for splitting water to produce hydrogen generally require a lot of energy at the time the hydrogen is generated. But our method allows us to produce hydrogen without supplying heat, connecting a battery, or adding electricity. Once the aluminum clusters are synthesized, they can generate hydrogen on demand without the need to store it.”
aluminum clusters
Figure 2 -- Gas generation: Images show
a water molecule splitting on surface of
aluminum cluster (bottom) and release of H2
(top left).
Source: VCU/PSU, image by A. C. Reber.

“Our previous research suggested that electronic properties govern everything about these aluminum clusters but this new study shows that it is the arrangement of atoms within the clusters that allows them to split water,” explains Evan Pugh, a professor in the Department of Chemistry and Physics at PSU. “Generally, this knowledge might allow us to design new nanoscale catalysts by changing the arrangements of atoms in a cluster. The results could open up a new area of research not only related to splitting water but also to breaking the bonds of other molecules as well.”

The team of researchers found that a water molecule will bind between two aluminum sites in a cluster so long as one behaves like a Lewis acid and the other like a Lewis base. The Lewis acid aluminum binds to the oxygen of the water molecule while the Lewis base dissociates a hydrogen atom. Figure 2 shows the process, with orange and blue spheres indicating the paired active sites that cause reactivity. Freeing a hydrogen atom leads to generation of hydrogen gas.

“It looks as though we might be able to come up with ways to remove the hydroxyl group (OH-) that remains attached to the aluminum clusters after they generate hydrogen so that we can reuse the aluminum clusters again and again,” concludes Khanna.
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