The global shipping industry is alone responsible for three percent of the total greenhouse gas emissions humans produce. If nothing is done to make shipping green, in a few decades, this sector will produce over 10 percent of the emissions.   

A new study from MIT researchers reveals a practical and scalable solution to this problem. The study authors have devised an emission-free approach to produce green hydrogen fuel for maritime applications such as boats, naval ships, commercial vessels, and even submarines.   

What’s even more interesting are the ingredients the researchers used. They claim that they can make hydrogen fuel using old soda cans, seawater, and caffeine. 

Two key challenges with hydrogen fuel

This isn’t the first study proposing the use of aluminum (which soda cans are made from) for producing hydrogen fuel. It is already well known that when aluminum and water react, hydrogen is formed as one of the byproducts. However, such reactions only work when aluminum is used in its pure state. After the first reaction, a layer of oxide covers the aluminum surface, blocking further reactions.

Scientists can use alloys such as gallium and indium to purify aluminum, but such are expensive and rare.

Another problem with hydrogen fuel is that it’s highly inflammable.

“One drawback to fueling vehicles with hydrogen is that some designs would require the gas to be carried onboard like traditional gasoline in a tank — a risky setup, given hydrogen’s volatile potential,” the study authors note. 

The study authors claim their approach can solve both of these challenges. It allows the reusing of gallium and indium alloys for repeated aluminum purification. Plus, one need not transport volatile hydrogen fuel from a production facility to a vessel as their method will enable a vehicle or a ship to produce and use hydrogen fuel on the go.

Making hydrogen gas using soda cans

During their study, the researchers turned old soda cans into pebble-sized aluminum pellets. They treated the pellets with an alloy (gallium or indium) to remove any impurities and then allowed the pellets to react with filtered seawater. 

This interaction resulted in the production of hydrogen gas. However, there was still one limitation — the reaction occurred at a slow rate, taking hours to produce hydrogen.

The study authors experimented with different chemicals including the ones that are typically found in kitchens to overcome this challenge. They soon realized that adding caffeine boosted the speed of hydrogen production. 

“The team discovered that a low concentration of imidazole (C3N2H4) — 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 added stimulant,” the study authors note.

Moreover, imidazole and the salt-water ions in the seawater enabled the researchers to recover and reuse more than 90 percent of the gallium-indium alloy. This is very important because the availability of rare-metal alloys is what makes green hydrogen production an expensive and unscalable process.

It may surprise you, but even today about 95 percent of all the hydrogen produced by humans involves the use of non-renewable sources such as coal and gas. With this approach, one can not only produce hydrogen without using fossil fuels, but also achieve cost-effective, scalable, and sustainable hydrogen-fuel production.

Application of seawater-based hydrogen fuel 

Since ships and submarines already have access to seawater, the proposed method has the potential to provide ample clean hydrogen power to all kinds of surface vessels and underwater vehicles. All they would need are some aluminum and caffeine, ingredients that are much cheaper and easier to transport than fossil fuels.

The study authors are currently working on a reactor that would follow their method to produce hydrogen on a moving vessel. 

“The vessel would hold a supply of aluminum pellets (recycled from old soda cans and other aluminum products), along with a small amount of gallium-indium and caffeine. These ingredients could be periodically funneled into the reactor, along with some of the surrounding seawater, to produce hydrogen on demand,” the study authors said.

They estimate that the hydrogen fuel produced by such a reactor using 40 lbs (18.14 kg) of aluminum would be enough to power an underwater glider for 30 days.

“We’re showing a new way to produce hydrogen fuel, without carrying hydrogen but carrying aluminum as the ‘fuel. 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 the ambient humidity to produce hydrogen. That’s down the line,” Aly Kombargi, lead study author and a PhD student at MIT, said.

The study is published in the journal Cell Reports Physical Science.