A. Welford Castleman Jr., Eberly Family Distinguished Chair in Science and Evan Pugh Professor in the Penn State Departments of Chemistry and Physics and Penn State graduate students Patrick Roach and Hunter Woodward and Virginia Commonwealth University Professor of Physics Shiv Khanna and postdoctoral associate Arthur Reber announced a discovery to produce hydrogen from water by exposing selected active sites of aluminum atoms on a nanoscaled aluminum cluster.
You might remember that aluminum when prepared can seize the oxygen of water and release the hydrogen. The problems have been generally in the energy costs for preparation of the aluminum and the recycling of it to reuse the metal after the oxygen has reacted enough to stop the oxidation process. In prior attempts and efforts to make an industrial model the electricity required to reprocess the metal and the bulk of the aluminum needed to do processing in significant amounts posed barriers. That and the hydrogen storage and fuel cell systems remain short of the maturity to get to consumer scaled markets. So solving the recycling energy needs and the bulk are prime targets to use the attributes of aluminum in a hydrogen release process.
In the research the group investigated the reactions of water with individual aluminum clusters by combining them under controlled conditions in a custom-designed flow-reactor. They found that a water molecule will bind between two active sites in an aluminum cluster as long as one of the sites behaves like a Lewis acid, a positively charged center that wants to accept an electron, and the other behaves like a Lewis base, a negatively charged center that wants to give away an electron. The Lewis-acid aluminum binds to the oxygen atom of the water and the Lewis-base aluminum dissociates a hydrogen atom. If this process happens a second time with another set of the two aluminum sites and a water molecule, then two hydrogen atoms are available, which then can join to become hydrogen gas.
The group demonstrated that it is the geometries of these aluminum clusters, rather than solely their electronic properties, that govern the proximity of the clusters’ exposed active acid and base sites. The proximity of the clusters’ exposed sites plays an important role in affecting the clusters’ reactions with water. Castleman said, “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. 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.”
Professor Khanna expands the description explaining the aluminum clusters react differently when exposed to water, depending on the sizes of the clusters and their unique geometric structures. Three of the aluminum clusters produced hydrogen from water at room temperature. He says, “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. 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 to a battery, or adding electricity. Once the aluminum clusters are synthesized, they can generate hydrogen on demand without the need to store it.”
Professor Khanna offers that the findings will pave the way toward investigating how the aluminum clusters can be recycled for continual usage and how the conditions for the release of hydrogen can be controlled. “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.”
This news is a significant distance forward from the observations of hydrogen releases in aluminum to what may be a workable process to produce hydrogen gas in significant amounts on demand. There is a lot of hydrogen production now, primarily from splitting the hydrogen from natural gas. An economical process powered by small energy requirements that recycles its main catalysts perhaps eternally from water would certainly change the calculations of almost all carbon and hydrogen uses in the various possible combinations.
There is a lot of carbon around and a great deal of catalyst reaction know-how already on hand. The problem has been getting the hydrogen from a very low cost and very low energy process. This news is welcome indeed and is showing good fundamentals in projecting a potential industrial process in the future.
The study paper was published in the 23 January 2009 issue of the journal Science and was funded and supported by the Air Force Office of Scientific Research.
Good job! There just might be one or perhaps someday, many catalyst processes that can compete with fossil resources.