MIT engineers draw hydrogen from soda cans, seawater, and caffeine

Engineers from the famous Massachusetts Institute of Technology (MIT) in Boston have found a method for creating pure hydrogen at sea that might become an interesting new path for greening the shipping industry. The technique uses recycled aluminum from soda cans, seawater, and… caffeine.

The engineers estimate that just 1 gram of aluminum would generate 1.3 liters of hydrogen in five minutes. The hydrogen could then fuel an onboard engine to drive a motor or generate electricity with a fuel cell to power the ship.

Powering a small submarine

The researchers believe they have the essential ingredients to build a sustainable hydrogen reactor that could be used in ships and underwater vehicles. They’ve calculated that such a reactor, holding about 20 kg of aluminum pellets, could power a small submarine for about 30 days while using the surrounding seawater.

The idea looks promising, as it wouldn’t require ships to have huge tanks to store hydrogen. Today, this can be done by compressing the gas at 350 bar (5,000 psi) or 700 bar (10,000 psi), as used for vehicles, or by liquefying it by reducing its temperature to −253°C.

The study, published in the Cell Reports Physical Science journal, was authored as a lead writer by Aly Kombargi, a PhD student in MIT’s Department of Mechanical Engineering. It was co-authored by Enoch Ellis, an undergraduate in chemical engineering; Peter Godart, PhD from ’21, who has founded a company to recycle aluminum as a hydrogen fuel source; and Douglas Hart, MIT professor of mechanical engineering, who leads the team.

So how does it work?

When activated correctly, aluminum reacts with water to generate hydrogen gas, heat, and aluminum oxyhydroxide, a non-toxic and valuable commodity. But it can only do so in a pure, exposed state.

The instant aluminum meets with oxygen, such as in air, the surface immediately forms a thin, shield-like layer of oxide that prevents further reactions. That’s why a soda can thrown into the water won’t start ‘bubbling’ on its own.

Rare metal alloy

That ‘barrier’ has to be penetrated with a small amount of rare metal alloy made from a specific concentration of gallium and indium. Gallium is a soft, silvery-white metal, similar to aluminum, often used in semiconductors. Indium is a smooth, malleable metal with a brilliant luster used for transistors and other electronic components.

The metal alloy serves as an ‘activator,’ scrubbing away any oxide buildup and creating a pure aluminum surface that is free to react with water. In the lab, a pebble-sized aluminum pellet pretreated with the alloy can react with filtered seawater to generate hydrogen.

Speeding up with caffeine

However, the reaction was much slower than with de-ionized water, where one pretreated aluminum pellet produced 400 milliliters of hydrogen in just five minutes. The researchers tried various unconventional ingredients to speed up the reaction in seawater.

“We were just playing around with things in the kitchen and found that when we added coffee grounds to seawater and dropped aluminum pellets in, the reaction was quite fast compared to just seawater,” lead author Aly Kombargi says.

When they asked their colleagues in MIT’s chemistry department for an explanation, they suggested trying imidazole—an active ingredient in caffeine—which happens to have a molecular structure that can pierce aluminum. This allows the material to continue reacting with water while keeping the gallium-indium’s ionic shield intact.

Recovering precious alloy

That was a significant breakthrough, as it made it possible to recover the expensive gallium-indium alloy by scooping it off when the process was finished. Now, it’s a matter of scaling up and industrializing the process, which is often the most challenging part after leaving the lab.

But Aly Kombargi is confident. “We’re showing a new way to produce hydrogen fuel, without carrying hydrogen but carrying aluminum as the fuel. The next part is figuring out how to use this for trucks, trains, and airplanes. Perhaps, instead of carrying water, we could extract water from the ambient humidity to produce hydrogen. That’s down the line.”