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19 hours ago
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Electric vehicles are becoming commonplace on roads worldwide, but powering larger-scale transportation—such as trains, ships, and airplanes—has remained a major technological challenge.
Now, new research from MIT may offer a breakthrough solution using an innovative fuel cell system that could outperform traditional batteries in energy-to-weight efficiency. Rather than trying to push lithium-ion battery technology to new extremes, the MIT team is developing a novel fuel cell that uses inexpensive liquid sodium metal. Instead of recharging, the system replaces the spent sodium fuel.
Fuel Cell Design
The proposed fuel cell features two separate chambers, one containing liquid sodium metal and the other filled with air. Sodium atoms pass through a solid ceramic electrolyte barrier to react with oxygen at a porous electrode on the air side. This chemical reaction generates electricity and, in prototype tests, produced three times the energy-to-weight ratio of lithium-ion batteries.
“We expect people to think that this is a totally crazy idea,” says co-author Yet-Ming Chiang, the Kyocera Professor of Ceramics. “If they didn’t, I’d be a bit disappointed because if people don’t think something is totally crazy at first, it probably isn’t going to be that revolutionary.”
Electric Vehicle Needs
Chiang sees the most significant advantage with electric aircraft, a field that particularly benefits from weight optimization. Such a weight reduction as the MIT team is offering may be a massive step toward making the large-scale implementation of electric airplanes a practical reality.
“The threshold that you really need for realistic electric aviation is about 1,000 watt-hours per kilogram,” Chiang says. Today’s electric vehicle lithium-ion batteries top out at about 300 watt-hours per kilogram — nowhere near what’s needed. Even at 1,000 watt-hours per kilogram, he says, that wouldn’t be enough to enable transcontinental or trans-Atlantic flights.
Chiang says the most common type of aviation, regional jaunts, could be run on a 1,000 watts per kilogram battery. These short-hops produce 30 percent of aviation emissions, accounting for 80 percent of domestic air traffic. Additionally, other large-scale systems, such as marine vehicles and rail, could also benefit from such technology.
“They all require very high energy density, and they all require low cost,” he says. “And that’s what attracted us to sodium metal.”
Maximizing Energy Density
For decades, researchers have attempted to develop rechargeable lithium-air or sodium-air batteries, attracted by their theoretical energy density.
“People have been aware of the energy density you could get with metal-air batteries for a very long time, and it’s been hugely attractive, but it’s just never been realized in practice,” Chiang says.
Instead of a conventional sealed battery, the MIT team applied the same electrochemical principles to a fuel cell, allowing reusability through fuel replacement rather than recharging.
Constructing the Prototypes
The team developed two prototype designs. One used a vertical glass tube structure with a central solid ceramic electrolyte and a porous air electrode, flanked by separate tubes for liquid sodium and air. The reaction occurred in the central tube as sodium fuel was gradually consumed.
In the second design, the chambers were horizontal. A tray held the sodium fuel above the ceramic electrolyte and air electrode. Testing showed the system could achieve up to 1,700 watt-hours per kilogram under controlled humidity—well above the targeted 1,000 watt-hour benchmark.
Cleaner Byproducts
The researchers envision stacking fuel cells like cafeteria trays in an aircraft. As the sodium is consumed, a byproduct stream—akin to jet exhaust—would emit sodium oxide instead of carbon dioxide. This compound could react in the atmosphere to form sodium bicarbonate (baking soda), potentially helping neutralize the acidity of greenhouse gases in water.
“There’s this natural cascade of reactions that happens when you start with sodium metal,” Chiang says. “It’s all spontaneous. We don’t have to do anything to make it happen, we just have to fly the airplane.”
Chiang also emphasized the safety of the design. Traditional batteries risk catastrophic failure if barriers between reactive materials break. In contrast, the MIT fuel cell has air on one side, reducing the risk of dangerous interactions.
From Lab to Market
While the prototype consists of a single cell, Chiang says scaling up the system will be straightforward. A spinoff company, Propel Aero, has already been formed to commercialize the technology.
Historically, the U.S. produced 200,000 tons of sodium metal annually for use in leaded gasoline—before ethanol became the standard. Although current production is far lower, sodium is easily sourced from common salt and has a low melting point (98°C), making it easier to handle and refuel.
The team’s next goal is to power a large drone using a single 1,000-watt-hour fuel cell—about the size of a brick. They expect to conduct liftoff tests within the next year.
The paper “Sodium-Air Fuel Cell for High Energy Density and Low-Cost Electric Power” appeared on May 27, 2025, in Joule.
Ryan Whalen covers science and technology for The Debrief. He holds an MA in History and a Master of Library and Information Science with a certificate in Data Science. He can be contacted at [email protected], and follow him on Twitter @mdntwvlf.
