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MIT Team Creates Clean Hydrogen with Seawater, Soda Cans, Caffeine

The engineers believe they have discovered the recipe for running a sustainable hydrogen reactor, which they plan to test first in marine and underwater vehicles.

Published 4 months ago | About a 5 minute read

Image: Researcher Aly Kombargi holds a jar of aluminum pellets as they start to react in seawater. | Tony Pulsone

A research team at MIT has discovered a simple, low-cost, sustainable method for creating clean hydrogen — with just seawater, soda cans and caffeine.

The team of engineers found that when the aluminum in soda cans is exposed in its pure form and mixed with seawater, the solution bubbles up and naturally produces hydrogen — a versatile gas that can be used to power an engine or fuel cell without generating carbon emissions. What the team also discovered is that this simple reaction can be sped up by adding a common stimulant: caffeine.

When exposed to air or water, pure aluminum instantly forms a protective, aluminum-oxide skin that keeps it from reacting with water: “This is why when you put a soda can in water, it doesn’t react,” explains Aly Kombargi — a PhD student in MIT’s Department of Mechanical Engineering and lead author of the study.

As described in Cell Reports Physical Science, the researchers were able to prevent this reaction and produce hydrogen gas by dropping pre-treated, pebble-sized aluminum pellets into a beaker of filtered seawater. The aluminum was pre-treated with a rare-metal alloy — a mix of gallium and indium — that prevents the formation of aluminum oxide, leaving pure aluminum that can react with seawater to generate hydrogen. The salt ions in the seawater can in turn attract and recover the alloy, which can be reused to generate more hydrogen, in a closed loop.

The team found that while this reaction between aluminum and seawater successfully produces hydrogen gas, it was a slow process. On a lark, they added coffee grounds to the mix and were surprised to see that it sped up the reaction. Turns out, a low concentration of imidazole, an active ingredient in caffeine, is enough to significantly speed up the reaction — producing the same amount of hydrogen in just five minutes, compared to two hours without the stimulant.

The researchers are developing a small reactor that could run on a marine vessel or underwater vehicle. The vessel would hold a supply of aluminum pellets (recycled from old soda cans and other aluminum products), along with a small amount of the gallium-indium mix and caffeine. These ingredients could be periodically funneled into the reactor, along with some of the surrounding seawater, to produce hydrogen on demand — which could then power an onboard engine or generate electricity to power the ship.

“This is very interesting for maritime applications like boats or underwater vehicles, because you wouldn’t have to carry around seawater — it’s readily available,” Kombargi says. “We also don’t have to carry a tank of hydrogen. Instead, we would transport aluminum as the ‘fuel,’ and just add water to produce the hydrogen that we need.”

Pitfalls of conventional hydrogen production and use

A fully decarbonized energy system will require both clean electrification and low-carbon fuels, and clean hydrogen holds great promise in enabling us to achieve a net-zero future — if we are able to efficiently and effectively scale its production. Hydrogen is increasingly seen as a potential substitute for fossil fuels, especially in energy-intensive processes that cannot easily be fueled by electricity — such as blast furnaces, cement works and industrial heating — and long-distance aviation and shipping.

But until now, hydrogen has had to be manufactured — usually by separating it from methane, which requires a lot of energy — which means it is only as clean as the energy sources used to make it. Most of the 70 million tons of hydrogen currently used globally each year by industry is derived from fossil fuels, giving it a large carbon footprint.

Energy companies such as Vattenfall are demonstrating the promise and viability of fossil-free hydrogen, but the International Energy Agency estimates we’ll need a six-fold increase in clean hydrogen production to achieve net zero by 2050.

The research team — led by Douglas Hart, MIT professor of mechanical engineering — is developing efficient, sustainable methods to produce hydrogen gas. The study’s co-authors also include Enoch Ellis, an undergraduate in chemical engineering; and Peter Godart, who earned his Mechanical Engineering PhD at MIT in 2021 and has co-founded Found Energy — a startup that recycles aluminum as a source of hydrogen fuel.

One barrier to fueling vehicles with hydrogen at scale is that some designs would require the gas to be carried onboard, like gasoline in a tank — a risky setup, given hydrogen’s volatile potential. Hart and his team have looked for ways to power vehicles with hydrogen without having to constantly transport the gas itself. Their aluminum-seawater-caffeine process is a promising workaround; but viability of the new system at scale would require a significant supply of gallium-indium, which is relatively expensive and rare.

“For this idea to be cost-effective and sustainable, we had to work on recovering this alloy post-reaction,” Kombargi says.

Closing the loop

The team found they could retrieve and reuse gallium-indium using a solution of ions, which protect the metal alloy from reacting with water and help it to precipitate into a form that can be scooped out and reused.

“Lucky for us, seawater is an ionic solution that is very cheap and available,” said Kombargi, who was able to duplicate the results with seawater from a nearby beach.

The researchers believe they have discovered the recipe for running a sustainable hydrogen reactor, which they plan to test first in marine and underwater vehicles. They’ve calculated that such a reactor — holding about 40 pounds of aluminum pellets — could power a small, underwater glider for roughly 30 days by pumping in surrounding seawater and generating hydrogen to power the motor.

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