A recent discovery by U.S. Army researchers is fueling excitement that aluminum could prove a potent source of energy, especially in remote or dangerous-to-access areas where resupply is difficult.
A few weeks ago, the U.S. Army Research Lab outlined results of a chance discovery, which the main researchers on the project described to S&P Global Market Intelligence in a recent interview. As they tell it, the team had developed a type of powder made from an aluminum alloy. They did not intend to use it to make fuel.
But they happened to pour water over it, and to their surprise, it bubbled almost immediately, reacting and spewing hydrogen gas, which can power a fuel cell. Fuel cells are like batteries but depend on chemical energy, typically hydrogen, to create electricity.
The chemistry in the reaction with aluminum is nothing new, the researchers acknowledged. But its speed and advantages over other known methods to produce hydrogen may be.
While most hydrogen produced today is extracted from fossil fuels, it has long been understood that if aluminum is allowed to react with water, it can, under certain circumstances, produce hydrogen gas through hydrolysis, the splitting of hydrogen and oxygen that make up water.
There are several ways to do this with aluminum, which are well researched.
Just adding a bit of scrap aluminum to water will not result in much of anything, at least not quickly.
To make water split and release hydrogen typically requires a special alloy of aluminum, such as with gallium, or the use of a catalyst, often a caustic substance, that is added to the water to start the reaction.
The reason for this, as researchers noted, is to prevent aluminum, which is a great store of energy, from oxidizing at its surface in the water and shutting down the reaction.
But what surprised the Army researchers was that their aluminum alloy powder, without a toxic catalyst, started and completed the reaction quickly. This has long been one of the key hurdles with aluminum as a means to create hydrogen on demand to power a fuel cell.
Without depending on a toxic catalyst, it typically takes time to get hydrogen via hydrolysis of water.
"Ours is the first [method] that I am aware of that accomplishes the same goal without any of these catalysts," said Scott Grendahl, one of the Army researchers on the team that made the discovery.
The findings are at a very early stage and will need a lot more testing, the team acknowledged. The excitement about the aluminum alloy powder stems from its potential to provide another source of energy, especially in tough or remote situations.
The advantages of using the aluminum powder over traditional power sources, or typical sources of hydrogen, may not seem obvious at first. But to a soldier, someone in a remote area or a company working on a remote project, they may spring to mind.
As the army researchers note, soldiers on away missions, who depend on an array of technology that requires energy, are limited to just a few days of power without packing extra battery packs. But with the powder and a bit of water, they might recharge their batteries using fuel cell technology.
Using aluminum may also eliminate some danger in depending on conventional fuels on the battlefield. Many deaths in war zones occur during resupply convoys, the researchers said. Aluminum powder, benign and nonexplosive, could be air-dropped, unlike liquid fossil fuels. This might help at tenuously held strongholds in a war zone where a ground convoy could easily come under attack.
Another benefit is that the powder might be produced relatively easily in the field using scavenged sources of aluminum, such as from the wreckage of a blown up tank or some other vehicle. Grendahl, while not going into specifics, said manufacturing the powder is straightforward.
"It's not a lengthy and difficult process," Grendahl noted. "We can make kilograms an hour."
The researchers also envision robots, in part built out of the aluminum powder, that can be used in 3-D printing, cannibalizing their own parts to keep critical systems going in dire situations.
And more generally, using aluminum to make hydrogen on the spot to power a fuel cell eliminates the need to store or transport highly explosive hydrogen under pressure. Jerry Woodall, a scientist who was not involved in the study but who researches hydrogen production, called this one of the chief advantages of the technology.
"You make hydrogen on demand, which is the most important thing about using aluminum technology," said Woodall, who holds a patent on an aluminum-gallium alloy that reacts with water to produce hydrogen.
Woodall also emphasized that aluminum is easy to get and recyclable, among other things. "The beautiful part of using aluminum to split water is that it's abundant, it's light and it has a high energy content," he said. "Those are the three things."
Woodall declined to comment on the Army research, given the lack of technical details about the process.
Water is needed to make the reaction happen, something that may be hard to come by in arid places. That is not necessarily a limitation even lacking a reliable water source such as a stream, lake or even the ocean. Any kind of liquid containing water, including urine, works to make the reaction start using the Army's aluminum alloy powder.
"So they would be carrying less weight," said Kristopher Darling, one of the researchers involved in the discovery, referring to soldiers who might not want to waste water supplies or carry heavy battery packs.
The end product of the reaction is aluminum hydroxide or oxide, also known as alumina, both of which can be recycled back to aluminum. The army researchers said the waste produced could also be safely dumped.
So far, the researchers have been tight-lipped about the finer details of the powder ingredients. They are applying for patents and said they have been contacted by a number of people interested in the findings and the potential applications.
They would only say the alloy includes one or more elements beyond aluminum. "In this case, we've taken two materials, or more materials ... and we've added a special element or two to the mix, and our processing disperses the two on a very, very fine link scale," Darling said, referring to the bonding of the elements.
The fine dispersion likely accounts for the quick start of the reaction, which the team believes may be the key breakthrough in its method, alongside the fact it does not require a toxic catalyst.
A video of how the powder can be used shows that speed at play in powering a remote-controlled tank. A researcher adds the powder to a cylinder, pours in a bit of water and screws the cylinder to the side of the small remote-controlled tank. Then he drives the tank, which is run by a hydrogen fuel cell.
"It is a very fast and aggressive reaction," said Anit Giri, a member of the research team.