Sustainable clean energy may lie in old cans and seawater.

Engineers at the Massachusetts Institute of Technology have discovered that when cans are exposed to seawater, the aluminum inside causes the solution to produce bubbles and naturally generate hydrogen gas—this gas can be used in engines or fuel cells without producing carbon emissions. More importantly, the addition of a very common stimulant—caffeine—can also speed up this simple reaction.

In a study published on July 25 in the journal Cell Reports Physical Science, researchers showed that they could generate hydrogen by dropping pre-treated, pebble-sized aluminum particles into a cup of filtered seawater.

These aluminum particles have been pre-treated with a rare metal alloy that can effectively purify into pure aluminum capable of reacting with seawater to produce hydrogen. The salt ions in the seawater can attract and recycle this alloy, allowing it to be reused in a sustainable cycle to generate more hydrogen.The team observed that the reaction between aluminum and seawater could successfully produce hydrogen, but at a slow rate. On a whim, they added some coffee grounds to the reaction mixture, and to their surprise, this action actually accelerated the reaction.

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Ultimately, the research group found that a low concentration of imidazole—a bioactive component in caffeine—was sufficient to speed up the reaction, producing as much hydrogen in just five minutes as would be produced in two hours without the stimulant.

Researchers are developing a small reactor that can operate on sea vessels or underwater vehicles. These containers will store a certain amount of aluminum balls (recycled from old cans and other aluminum products), as well as a small amount of gallium-indium and caffeine. These ingredients are periodically injected into the reactor along with the surrounding seawater to produce hydrogen on demand, thus providing fuel for the ship's engines or power for the vessel.

"For maritime applications like ships or underwater vehicles, this is very interesting because you don't have to carry seawater with you—it's available everywhere," said Aly Kombargi, the lead author of the study and a doctoral student in the Department of Mechanical Engineering at MIT. "We also don't have to carry a tank of hydrogen. Using aluminum as 'fuel,' we can produce the hydrogen we need just by adding water."

The co-authors of this study include Enoch Ellis, an undergraduate student majoring in chemical engineering, Dr. Peter Godart, who founded a company that recycles aluminum as a source of hydrogen fuel, and Professor Douglas Hart from the Department of Mechanical Engineering at MIT.Protective Layer Activation

A team led by Hart at the Massachusetts Institute of Technology is developing an efficient and sustainable method for hydrogen production. Hydrogen is regarded as a "green" energy source that can power engines and fuel cells without producing emissions that contribute to climate warming.

One drawback of using hydrogen as a fuel for vehicles is the need to store the gas in a tank similar to conventional gasoline—given the volatility of hydrogen, such a design poses risks. Hart and his team instead sought a way to power vehicles without the continuous transportation of hydrogen.

They found a viable solution in aluminum—a naturally abundant and stable material that, when in contact with water, undergoes a chemical reaction to produce hydrogen and heat.

However, this reaction presents a dilemma: although aluminum can produce hydrogen when mixed with water, it can only do so in a pure, exposed state. Once aluminum comes into contact with oxygen (such as the oxygen in the air), a thin layer of protective oxide forms immediately on the surface, preventing further reaction. This is why hydrogen does not immediately bubble out when you throw a soda can into water. This barrier is the reason why hydrogen does not immediately bubble when you throw a soda can into the water.In previous studies, the team found that by pre-treating aluminum with a rare metal alloy made of a small amount of gallium and indium at a specific concentration in fresh water, they could break through the protective layer of aluminum and maintain a reaction with water. This alloy acts as an "activator" to prevent the accumulation of oxides, creating a pure aluminum surface that can react with water.

When they conducted the reaction in fresh water and deionized water, they found that a pre-treated aluminum particle could produce 400 milliliters of hydrogen gas in just five minutes. They estimated that only 1 gram of aluminum particles could generate 1.3 liters of hydrogen gas in the same period.

However, to further scale up the system, a large supply of relatively expensive and rare gallium-indium alloy is needed. "To make this idea cost-effective and sustainable, we must find a way to recover this alloy after the reaction," said Kombirgi.

By the Sea

In the team's new research, they found that an ionic solution can be used to recover and reuse gallium-indium. Ions - charged atoms or molecules - can protect the metal alloy from reacting with water and help it precipitate into a form that can be scooped out and reused."We are fortunate that seawater is an ionic solution, very cheap and easily accessible," said Kombirgi, who tested the idea using seawater from a nearby beach. "I actually went to Revere Beach with a friend, and we filled bottles with water, then I filtered out the seaweed and sand, added aluminum, and it worked just as well."

He found that when he added aluminum to a beaker containing filtered seawater, there were indeed bubbles of hydrogen gas. And afterwards, he was able to scoop out the gallium indium. However, the reaction in seawater occurred much slower than in freshwater. It turns out that the ions in seawater acted as a shield for the gallium indium, allowing it to coagulate and be recovered after the reaction. But these ions also had a similar effect on aluminum, forming a barrier that slowed its reaction with water.

As they looked for ways to speed up the reaction in seawater, the researchers tried various unusual ingredients.

"We were just playing around in the kitchen and found that when we added coffee grounds to the seawater, then put in aluminum balls, the reaction was quite fast compared to just using seawater," Kombirgi said.

To understand the reason for the acceleration, the team turned to colleagues in the Chemistry Department at MIT, who suggested trying imidazole—a bioactive component of caffeine that just happens to have a molecular structure capable of penetrating aluminum (allowing the material to continue reacting with water) while maintaining the integrity of the gallium indium's ionic shield."This is a significant victory," Kombargi said. "We got everything we wanted: the recycling of gallium and indium, as well as a rapid and efficient reaction."

Researchers believe they have mastered the basic elements of running a sustainable hydrogen reactor. They plan to first test it on sea vessels and underwater vehicles. They calculated that such a reactor, equipped with about 40 pounds of aluminum balls, can provide about 30 days of power for a small underwater glider by extracting hydrogen gas from the surrounding seawater.

"This is a new method of producing hydrogen fuel, not carrying hydrogen gas, but using aluminum as 'fuel'," Kombargi said. "The next part is to figure out how to use it for trucks, trains, and airplanes. Perhaps, we no longer need to carry water, but can extract water from the surrounding humidity to produce hydrogen, which will be the direction of future development."