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Paving the Hydrogen Highway with Aluminum

Ah, if only our vehicle fuel was as abundant as say, water.

In his 2003 State of the Union address, former President George W. Bush proposed a $1.2 billion research initiative that would someday lead to a U.S. vehicle fleet weaned off petroleum and running on zero-emission hydrogen fuel cells. Six years later, this hydrogen-based economy envisioned by President Bush is still seems little more than dream. In fact, if it wasn't for Arnold Schwarzenegger's continuing push for a California Hydrogen Highway and Obama's brief mention of hydrogen on the campaign trail, you might think policymakers have long given up on transforming the nation's roadways to a hydrogen-fueled transportation grid.

Experts have long pointed to the high cost and effort required to launch a new vehicle fleet and build a storage and delivery infrastructure as obstacles to a hydrogen economy, but the production drawbacks of hydrogen itself is a bigger problem.
Proponents of hydrogen, a highly explosive gas (let us not forget the Hindenburg), call it a "clean burning" fuel as the only products of its reaction with oxygen are water, electricity, and heat. It may be clean burning, but its production methods are anything but.

Ninety-five percent of the 42 million tons of hydrogen consumed globally each year are produced from fossil fuels - processes that creates CO2 and other greenhouse gases as a byproduct. Further, all hydrogen production methods require large amounts of energy break the molecular bonds of hydrocarbons or water. With less than 1 percent of energy produced in the U.S. comes from renewable sources, most of this electricity comes from coal. This results in hydrogen being ‘clean-burning' fuel more environmentally harmful in production than beneficial in use.

But new research out of Penn State University and the Virginia Commonwealth University could change that. According to an article published in last week's Science, a team of five researchers have uncovered a new way to make hydrogen gas - one that uses less energy than previous production methods and which uses water, not fossil fuels, as the root stock for its hydrogen.

The team discovered three aluminum anion ‘clusters' (anions are atoms with more electrons than protons) capable of generating hydrogen gas from water at room temperature. The specific size and arrangement of these aluminum clusters are what allow the unique reaction to occur.

"The unique feature in the three aluminum clusters that produced hydrogen is that while they only have aluminum atoms, some Al sites act to absorb water molecules while the others help in breaking the water into H and OH units," said Virginia Commonwealth University physics professor Shiv Khanna.

Penn State professor Welford Castleman, Jr. elaborated, "The hydrogen production mechanism involves the proximity of two related reaction sites termed Lewis acid and Lewis base. When the water interacts with these, a hydrogen atom can be formed which is then free to react with a neighboring one and thereby form hydrogen gas." Lewis acids and bases are charged areas wanting to accept or give away an electron respectively; "Lewis" refers to the physical chemist, Gilbert Lewis, who first theorized the existence of covalent bonds.

Limitations of this new reaction, however, are that the aluminum clusters are difficult to produce in large quantities and, even then, can only be used once. To increase practicality, the research team will now search for ways to recycle the clusters. "It looks as though we may 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," Khanna said in a press release.

Should they be successful, this aluminum cluster reaction could someday affect the world's hydrogen market.

The researchers are quick to caution while there are no limitations on the use of the hydrogen produced in their reactions, their results cannot yet be applied on a mass scale. "We are dealing with very small quantities and only through future studies can reveal the prospects of applications," noted Castleman.