Hydrogen has the potential to be a climate-friendly fuel since it does not release carbon dioxide when used as an energy source. Currently, however, most methods for producing hydrogen involve fossil fuels, making hydrogen less of a 'green' fuel over its entire life cycle.

A new process developed by engineers could significantly shrink the carbon footprint associated with making hydrogen.

Last year, the MIT team reported that they could produce hydrogen gas by combining seawater, recycled soda cans, and caffeine. The question then was whether the benchtop process could be applied at an industrial scale, and at what environmental cost. 

MIT engineers have developed a new aluminium-based process to produce hydrogen gas, that they are testing on a variety of applications, including an aluminium-powered electric vehicle, pictured here. Image: Courtesy of the researchers.

Now, the researchers have carried out a 'cradle-to-grave' life cycle assessment, taking into account every step in the process at an industrial scale.

For instance, they calculated the carbon emissions associated with acquiring and processing aluminium, reacting it with seawater to produce hydrogen, and transporting the fuel to fuel stations, where drivers could tap into hydrogen tanks to power engines or fuel cell cars. They found that, from end to end, the new process could generate a fraction of the carbon emissions that is associated with conventional hydrogen production.

In a study that appeared recently in Cell Reports Sustainability, the team reports that for every kilogram of hydrogen produced, the process would generate 1.45 kilograms of carbon dioxide over its entire life cycle. In comparison, fossil-fuel-based processes emit 11 kilograms of carbon dioxide per kilogram of hydrogen generated.

The low-carbon footprint is on par with other proposed 'green hydrogen' technologies, such as those powered by solar and wind energy.

“We’re in the ballpark of green hydrogen,” says lead author Aly Kombargi PhD ’25, who graduated this spring from MIT with a doctorate in mechanical engineering. “This work highlights aluminium’s potential as a clean energy source and offers a scalable pathway for low-emission hydrogen deployment in transportation and remote energy systems.”

The study’s co-authors are Brooke Bao, Enoch Ellis, and professor of mechanical engineering Douglas Hart.

Gas bubble

Dropping an aluminium can in water will not normally cause much of a chemical reaction. That is because when aluminium is exposed to oxygen, it instantly forms a shield-like layer.

Without this layer, aluminium exists in its pure form and can readily react when mixed with water. The reaction that occurs involves aluminium atoms that efficiently break up molecules of water, producing aluminium oxide and pure hydrogen. And it does not take much of the metal to bubble up a significant amount of the gas. 

The new process starts with pellets of recycled aluminium (in jar) that react with seawater to produce pure hydrogen. The team found that if scaled up, the process could generate “green” hydrogen with a low-carbon footprint. Image: Tony Pulsone, MIT MechE.

“One of the main benefits of using aluminium is the energy density per unit volume,” says Kombargi. “With a very small amount of aluminium fuel, you can conceivably supply much of the power for a hydrogen-fuelled vehicle.”

Last year, he and Hart developed a recipe for aluminium-based hydrogen production. They found they could puncture aluminium’s natural shield by treating it with a small amount of gallium-indium, which is a rare-metal alloy that effectively scrubs aluminium into its pure form.

The researchers then mixed pellets of pure aluminium with seawater and observed that the reaction produced pure hydrogen. What is more, the salt in the water helped to precipitate gallium-indium, which the team could subsequently recover and reuse to generate more hydrogen, in a cost-saving, sustainable cycle.

“We were explaining the science of this process in conferences, and the questions we would get were, ‘How much does this cost?’ and, ‘What’s its carbon footprint?’” says Kombargi. “So we wanted to look at the process in a comprehensive way.”

A sustainable cycle

For their new study, Kombargi and his colleagues carried out a life-cycle assessment to estimate the environmental impact of aluminium-based hydrogen production, at every step of the process, from sourcing the aluminium to transporting the hydrogen after production.

They set out to calculate the amount of carbon associated with generating a kilogram of hydrogen – an amount that they chose as a practical, consumer-level illustration.

“With a hydrogen fuel cell car using one kilogram of hydrogen, you can go between 60km to 100km, depending on the efficiency of the fuel cell,” says Kombargi.

They performed the analysis using Earthster – an online life cycle assessment tool that draws data from a large repository of products and processes and their associated carbon emissions.

The team considered a number of scenarios to produce hydrogen using aluminium, from starting with 'primary' aluminium mined from the Earth, versus 'secondary' aluminium that is recycled from soda cans and other products, and using various methods to transport the aluminium and hydrogen.

After running life-cycle assessments for about a dozen scenarios, the team identified one scenario with the lowest carbon footprint. This scenario centres on recycled aluminium – a source that saves a significant amount of emissions compared with mining aluminium – and seawater – a natural resource that also saves money by recovering gallium-indium.

They found that this scenario, from start to finish, would generate about 1.45 kilograms of carbon dioxide for every kilogram of hydrogen produced. The cost of the fuel produced, they calculated, would be about $9 per kilogram, which is comparable to the price of hydrogen that would be generated with other green technologies such as wind and solar energy.

The researchers envision that if the low-carbon process were ramped up to a commercial scale, it would look something like this: the production chain would start with scrap aluminium sourced from a recycling centre.

Treated with gallium-indium

The aluminium would be shredded into pellets and treated with gallium-indium. Then, drivers could transport the pretreated pellets as aluminium 'fuel', rather than directly transporting hydrogen, which is potentially volatile.

The pellets would be transported to a fuel station that ideally would be situated near a source of seawater, which could then be mixed with the aluminium, on demand, to produce hydrogen. A consumer could then directly pump the gas into a car with either an internal combustion engine or a fuel cell.

The entire process does produce an aluminium-based byproduct, boehmite, which is a mineral that is commonly used in fabricating semiconductors, electronic elements, and a number of industrial products. Kombargi says that if this byproduct were recovered after hydrogen production, it could be sold to manufacturers, further bringing down the cost of the process as a whole.

“There are a lot of things to consider,” says Kombargi. “But the process works, which is the most exciting part. And we show that it can be environmentally sustainable.”

The group is continuing to develop the process. They recently designed a small reactor, about the size of a water bottle, that takes in aluminium pellets and seawater to generate hydrogen, enough to power an electric bike for several hours.

They previously demonstrated that the process can produce enough hydrogen to fuel a small car. The team is also exploring underwater applications, and are designing a hydrogen reactor that would take in surrounding seawater to power a small boat or underwater vehicle.