Hydrogen stands out as a promising climate-friendly fuel, primarily because it emits no carbon dioxide when used. However, the majority of hydrogen production techniques currently rely on fossil fuels, which diminishes its reputation as a truly green option throughout its life cycle.
Recently, a pioneering method developed by MIT engineers holds the potential to drastically reduce the carbon footprint of hydrogen production.
A year ago, the research team revealed their innovative approach, utilizing seawater, recycled aluminum cans, and caffeine to produce hydrogen gas. The pressing question was whether this laboratory process could be effectively scaled up for industrial use without incurring significant environmental costs.
The team conducted a comprehensive “cradle-to-grave” life cycle assessment, evaluating every stage of the production process at an industrial scale. They analyzed carbon emissions linked to sourcing and processing aluminum, reacting it with seawater to generate hydrogen, and transporting this fuel to gas stations for use in hydrogen-powered vehicles. Their findings indicate that this new method could produce only a fraction of the carbon emissions associated with traditional hydrogen production.
In a recent study published in Cell Reports Sustainability, the researchers revealed that each kilogram of hydrogen produced through their process results in only 1.45 kilograms of carbon dioxide emissions over the entire life cycle. Comparatively, conventional fossil-fuel-based methods release a staggering 11 kilograms of carbon dioxide for every kilogram of hydrogen.
This low-carbon footprint positions their method alongside other emerging “green hydrogen” technologies, such as those harnessing solar and wind power.
“We’re in the ballpark of green hydrogen,” states lead researcher Aly Kombargi, who earned his PhD in mechanical engineering from MIT this spring. He emphasizes aluminum’s significant potential as a clean energy source, offering a viable pathway for low-emission hydrogen deployment across transportation and remote energy applications.
The co-authors of the study from MIT include Brooke Bao, Enoch Ellis, and Professor Douglas Hart of the mechanical engineering department.
The Science Behind It
When an aluminum can is immersed in water, a notable chemical reaction typically doesn’t occur. This is due to a protective layer that forms on aluminum upon exposure to oxygen. However, if this layer is stripped away, the aluminum can react vigorously with water. This reaction allows aluminum atoms to efficiently break water molecules, producing aluminum oxide and pure hydrogen. Remarkably, only a small amount of aluminum can yield a considerable volume of hydrogen gas.
A year ago, Kombargi and Hart devised a formula for aluminum-based hydrogen generation. They found that treating aluminum with a small amount of gallium-indium—a rare metal alloy—creates a pure form of aluminum by removing its natural shield. When fine aluminum pellets are combined with seawater, the reaction produces pure hydrogen, and the salt aids in the recovery and reuse of gallium-indium, promoting a sustainable cycle.
Evaluating Sustainability
In the new study, Kombargi and his team performed a life cycle assessment to gauge the environmental impact of aluminum-based hydrogen production from start to finish. They aimed to ascertain the carbon emissions tied to generating 1 kilogram of hydrogen, a practical amount for consumer reference.
A hydrogen fuel cell car utilizing 1 kilogram of hydrogen can travel between 60 to 100 kilometers, depending on the fuel cell’s efficiency, according to Kombargi.
Utilizing Earthster, an online life cycle assessment tool, the team analyzed various scenarios for hydrogen production with aluminum, comparing the use of “primary” aluminum, sourced from mining, against “secondary” aluminum, which is recycled from products like soda cans. They also evaluated different transportation methods for aluminum and hydrogen.
Following this extensive analysis, the researchers pinpointed a specific scenario with the lowest carbon footprint. This scenario utilized recycled aluminum, drastically reducing emissions compared to mined aluminum, and combined it with seawater to optimize costs by recovering gallium-indium. They calculated that this approach would produce roughly 1.45 kilograms of carbon dioxide for every kilogram of hydrogen generated, with a production cost of about $9 per kilogram—competitive with hydrogen produced using other green technologies, including wind and solar.
If scaled commercially, the envisioned production chain would begin with scrap aluminum from recycling centers. The aluminum would be converted into pellets, treated with gallium-indium, and then transported as “aluminum fuel” to hydrogen stations near seawater sources. This setup would allow on-demand hydrogen production for consumer vehicles.
Despite generating aluminum-based byproducts like boehmite, which is valuable in the semiconductor and electronics industries, Kombargi points out the potential for additional cost savings by recovering this bioproduct after hydrogen production.
The team continues to refine their approach, having recently developed a compact reactor, roughly the size of a water bottle, capable of using aluminum pellets and seawater to generate hydrogen sufficient to power electric bikes for several hours. They’ve also demonstrated the capacity to produce enough hydrogen to fuel small cars and are exploring additional applications, including underwater vehicles.
This research was partially supported by the MIT Portugal Program.
Photo credit & article inspired by: Massachusetts Institute of Technology
