“`html

Hydrogen holds the promise of being an environmentally-friendly fuel as it does not emit carbon dioxide when utilized as an energy source. Nevertheless, most existing methods for hydrogen production currently rely on fossil fuels, which diminishes hydrogen’s reputation as a truly “green” fuel across its entire lifecycle.

A novel method crafted by MIT engineers has the potential to drastically reduce the carbon footprint tied to hydrogen production.

Last year, the group disclosed that they could generate hydrogen gas by merging seawater, recycled soda cans, and caffeine. The next inquiry was whether this benchtop method could be scaled to industrial levels and what environmental implications that would entail.

Now, the scientists have conducted a comprehensive “cradle-to-grave” lifecycle assessment, examining every phase of the process at an industrial scale. For example, the team assessed the carbon emissions linked to acquiring and processing aluminum, its reaction with seawater to generate hydrogen, and transporting the fuel to gas stations, where drivers could access hydrogen tanks to power engines or fuel cell vehicles. They discovered that, from start to finish, this new method could yield a small fraction of the carbon emissions typically associated with standard hydrogen production.

In a study published today in Cell Reports Sustainability, the researchers indicate that for every kilogram of hydrogen generated, the process would produce 1.45 kilograms of carbon dioxide over its full lifecycle. By contrast, fossil-fuel-derived methods release 11 kilograms of carbon dioxide for every kilogram of hydrogen produced.

The minimal carbon footprint is comparable to other proposed “green hydrogen” technologies, such as those harnessing solar and wind energy.

“We’re in the vicinity of green hydrogen,” remarks lead author Aly Kombargi PhD ’25, who graduated this spring from MIT with a doctorate in mechanical engineering. “This research illustrates aluminum’s potential as a clean energy source and provides a scalable pathway for low-emission hydrogen use in transportation and off-grid energy systems.”

The co-authors from MIT include Brooke Bao, Enoch Ellis, and mechanical engineering professor Douglas Hart.

Gas bubble

Dropping an aluminum can into water typically does not lead to a notable chemical reaction. This is because when aluminum encounters oxygen, it quickly forms a protective layer. In its unprotected state, aluminum can react readily with water. The resulting reaction involves aluminum atoms efficiently breaking down water molecules, generating aluminum oxide and pure hydrogen. Remarkably, it does not require much aluminum to produce a substantial quantity of the gas.

“One of the primary advantages of utilizing aluminum is the energy density per unit volume,” Kombargi explains. “With a tiny amount of aluminum fuel, you could theoretically provide a significant portion of the power needed for a hydrogen-powered vehicle.”

Last year, he and Hart formulated a method for aluminum-based hydrogen production. They discovered they could penetrate aluminum’s natural protective layer using a small quantity of gallium-indium, a rare-metal alloy that effectively purifies aluminum. The team then combined pellets of pure aluminum with seawater and observed that the reaction yielded pure hydrogen. Additionally, the salt in the water aided in precipitating gallium-indium, which the team could later recover and reuse to produce more hydrogen, maintaining a cost-efficient, sustainable cycle.

“We were explaining the science behind this process at conferences, and the inquiries we received were primarily about, ‘What’s the cost?’ and, ‘What’s the carbon footprint?’” Kombargi notes. “Thus, we aimed to analyze the process comprehensively.”

A sustainable cycle

For their recent study, Kombargi and his team conducted a lifecycle assessment to evaluate the environmental impact of aluminum-based hydrogen production at every stage, from sourcing the aluminum to transporting the hydrogen post-production. They aimed to calculate the carbon footprint associated with producing 1 kilogram of hydrogen—a figure they deemed a practical, consumer-level representation.

“With a hydrogen fuel cell vehicle using 1 kilogram of hydrogen, you can travel between 60 to 100 kilometers, depending on the fuel cell’s efficiency,” Kombargi points out.

They performed their analysis using Earthster, an online lifecycle assessment tool that accesses a vast database of products and processes along with their associated carbon emissions. The team evaluated multiple scenarios for hydrogen production using aluminum, comparing “primary” aluminum sourced from mining versus “secondary” aluminum recycled from soda cans and other products, along with various transport methods for both aluminum and hydrogen.

After assessing approximately a dozen scenarios, the team discovered one scenario that exhibited the lowest carbon footprint. This scenario focuses on recycled aluminum—a source that considerably minimizes emissions in contrast to extracting aluminum—and seawater, a natural resource that also reduces costs by recovering gallium-indium. They found that this scenario, from beginning to end, would emit about 1.45 kilograms of carbon dioxide for every kilogram of hydrogen produced. The estimated cost for this produced fuel would be around $9 per kilogram, which is on par with the pricing of hydrogen generated through other green technologies such as wind and solar energy.

The researchers predict that if this low-carbon process were to be scaled up to a commercial level, it could be structured like this: The production chain would commence with scrap aluminum sourced from a recycling hub. The aluminum would be shredded into pellets and treated with gallium-indium. Then, drivers would transport these pretreated pellets as aluminum “fuel,” rather than transporting hydrogen directly, which presents volatility risks. The pellets would be delivered to a fueling station ideally located near a seawater source, where they could then be mixed on demand to create hydrogen. Consumers could subsequently pump the gas into vehicles equipped with either internal combustion engines or fuel cells.

The overall process does yield an aluminum-based byproduct, boehmite, which is a mineral commonly utilized in the manufacture of semiconductors, electronic components, and various industrial products. Kombargi notes that if this byproduct is extracted after hydrogen production, it could be marketed to manufacturers, further reducing the overall costs of the process.

“There are numerous factors to weigh,” Kombargi states. “But the process functions, which is the most thrilling aspect. And we demonstrate that it can be environmentally sustainable.”

The group is actively working on further developing the process. They have recently designed a compact reactor, about the size of a water bottle, capable of using aluminum pellets and seawater to produce hydrogen sufficient to power an electric bicycle for several hours. Previously, they demonstrated that the process can generate enough hydrogen to fuel a small vehicle. The team is also investigating underwater applications and is designing a hydrogen reactor that would utilize surrounding seawater to power a small boat or underwater craft.

This research received partial support from the MIT Portugal Program.

“`