MIT researchers have developed a groundbreaking sodium–air fuel cell that could reshape the future of electric transportation. Designed to replace the heavy lithium-ion batteries currently used in aviation, marine, and rail sectors, this innovative system delivers more than three times the energy density of today’s electric vehicle (EV) batteries — potentially making electric flight a reality.
The new fuel cell, developed by a team led by MIT doctoral students Karen Sugano, Sunil Mair, Saahir Ganti-Agrawal, and Professor Yet-Ming Chiang, uses liquid sodium metal and ambient air as its core materials. Unlike traditional batteries, which are limited by their weight-to-energy ratio, this system offers a fuel cell format that can be quickly refueled and deliver sustained power output.
One of its most striking features is its environmental profile: the fuel cell emits no carbon dioxide. In fact, it actively captures CO₂ from the air, producing sodium bicarbonate — commonly known as baking soda — as a byproduct.
Fuel cells differ from batteries in one key way: while batteries store all of their energy internally and require recharging, fuel cells rely on a continuous input of fuel and oxidizer — in this case, sodium and air. A solid ceramic membrane allows sodium ions to move between compartments, while a specialized air electrode enables the electrochemical reaction that generates electricity.
MIT’s prototype achieved over 1,500 watt-hours per kilogram at the stack level, which translates to more than 1,000 watt-hours per kilogram at the full system level. For context, the best lithium-ion batteries today max out at around 300 watt-hours per kilogram — not nearly enough for electric planes or long-range ships.
“We expect people to think that this is a totally crazy idea,” said Professor Chiang, Kyocera Professor of Ceramics at MIT. “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.”
Chiang explains that the minimum threshold to make electric aviation practical is around 1,000 watt-hours per kilogram, especially for regional flights. Although not sufficient for transcontinental or intercontinental travel, this breakthrough could enable electric-powered short-haul flights, which make up a substantial portion of domestic air traffic and emissions.
The implications stretch beyond aviation. The marine and rail industries also demand high energy density and low operating costs — both of which this sodium–air fuel cell can deliver.
For decades, scientists have explored metal–air battery chemistries, especially lithium–air and sodium–air, due to their theoretical energy densities. However, making them reliably rechargeable has proven elusive. By shifting the focus from batteries to fuel cells — which are inherently refillable — the MIT team found a practical path forward.
The team built two types of lab-scale prototypes:
- H-cell design: Two vertical glass tubes joined by a ceramic-electrolyte bridge, separating liquid sodium on one side and airflow on the other.
- Horizontal cell: A tray-based layout where sodium interacts with air across a ceramic membrane.
Both setups confirmed the concept’s high energy potential and operational stability.
Perhaps the most novel feature of the sodium–air fuel cell is its carbon-negative footprint. The reaction produces sodium oxide, which, upon contact with air moisture, becomes sodium hydroxide. This compound then reacts with atmospheric CO₂ to create solid sodium carbonate and eventually sodium bicarbonate — a form of passive carbon capture.
For aircraft, Chiang envisions fuel packs inserted like food trays into compartments. As the sodium is consumed, the exhaust — instead of emitting greenhouse gases — would help remove CO₂ from the air, creating a fundamentally cleaner energy cycle.
While this technology is still in its experimental phase, its potential to dramatically increase energy density while reducing emissions makes it a promising candidate for next-generation transportation systems. If further developed, sodium–air fuel cells could usher in a new era of electrified transport — from skies to seas to railways — with significantly less environmental impact.
By Impact Lab
