NEWS
Sustainable Flight Redefined
A fuel cell with a three-fold boost over current electric vehicle batteries could be the key to electrified ships and planes. Written by Nicole Imeson
WITH THE POTENTIAL TO STORE more power by weight than current battery iterations, a new fuel cell concept could help electrify transportation systems beyond the road.
Researchers at the Massachusetts Institute of Technology have developed a new class of aviation fuel cells that outperform standard batteries and take up less space than hydrogen systems. Backed by the U.S. Department of Energy’s ARPA-E PROPEL-1K program, the team set out to develop sodium-to-air fuel cells that delivered 1,000 watt-hours per kilogram, double the target of the previous Battery500 benchmark for electric cars. This energy density would enable regional flights to travel up to 300 miles and offer a clear path to slashing emissions in short-haul aviation.
ALL IN THE REACTION
The fuel cell pulls sodium toward oxygen in the air, which naturally drives the reaction forward. As liquid metal sodium contacts the ceramic membrane, the material passes through only positively charged sodium ions. Negative charges move through an external circuit, producing electricity. Once through the membrane, sodium ions react with oxygen, water vapor, returning electrons to form liquid sodium hydroxide. The byproduct evolves further as the cell discharges, first into sodium carbonate when exposed to atmospheric carbon dioxide (CO₂), then into sodium bicarbonate with added moisture.
“Sodium hydroxide helps capture CO₂ from the air and deacidify ocean water. The potential for a harmless, even beneficial, discharge product drew us to this approach,” explained Yet-Ming Chiang, Kyocera Professor of Ceramics and Materials Science at MIT.
An H-cell modified with electrodes and an ion-conducting ceramic membrane to conduct sodium-air fuel cell experiments. Photo: Gretchen Ertl/MIT
Since sodium reacts with air outside the cell, the byproduct forms externally and allows simple removal, enabling a design that mimics the convenience of disposable batteries. The fuel cell sustains continuous operation and preserves high energy density by carefully managing humidity levels on the air-facing side. Hygroscopic sodium hydroxide absorbs moisture and flushes out as a liquid. Early tests confirmed that ambient humidity in most climates triggered the reaction, although dry conditions could require added humidification. This strategy prevents the solid discharge buildup that historically plagued metal-to-air battery systems.
Instead of relying on solid metal or gas reactants, the fuel cell uses liquid sodium metal, which melts at 98 °C (208 °F). “We operated the fuel cell between 110-120 °C (230-248 °F). During discharge, the cell ran at 80 to 90 percent efficiency. The remaining energy converted into heat could help to keep the sodium molten,” Chiang said.
The discharge chemistry provides a unique environmental advantage. When aerosolized, sodium hydroxide can capture CO₂ from the air in under 12 seconds. In an open system, the researchers envision this process unfolding in real time by dispersing the discharge product freely into the atmosphere. This setup creates the potential for carbon credits, which could offset the cost of fuel and reinforce the system’s role in climate mitigation.
Alternatively, in a closed system, the team collected sodium hydroxide for industrial use or point-source carbon capture. “The open system would behave more like a fossil-fueled airplane, heaviest at takeoff, then lightening as it flies,” Chiang explained.
The research team, from left: Saahir Ganti-Agrawal, Karen Sugano, Sunil Mair, and Yet-Ming Chang. Photo: Gretchen Ertl/MIT
“Sodium hydroxide helps capture carbon dioxide from the air and deacidify ocean water. The potential for a harmless, even beneficial, discharge product drew us to this approach.”
—Yet-Ming Chiang, Kyocera Professor of Ceramics and Materials Science at MIT
DENSITY AND MODULARITY
Early testing showed cells delivering 2 volts each. “To meet higher system voltages, we would stack individual fuel cells in series. A 400-volt application would require 200 cells,” Chiang explained. Each unit features a ceramic membrane, an air cathode, and a liquid sodium core. The fuel cells can be built with modular simplicity, using refillable sodium metal cartridges to reduce waste and cost. Researchers are also designing assemblies to trim weight and improve manufacturability, pushing toward scalable deployment.
Sodium offers more than just technical performance. As one of Earth’s most abundant elements, it costs little and has in past decades been produced and distributed widely. A technoeconomic analysis showed the sodium-air fuel cell matched conventional jet fuel on cost of delivered energy, while outperforming green hydrogen, ammonia, and sustainable aviation fuels in both price and practicality.
A vial of liquid molten sodium metal. Photo: Gretchen Ertl/MIT
Previous metal-to-air fuel cells relied on lithium but demanded pure oxygen and produced byproducts that neither helped the environment nor reverted easily to metal, limiting rechargeability. Solid deposits formed during discharge and clogged systems, cutting performance. The sodium-to-air fuel cell avoids these pitfalls by reacting with ambient air and preventing solid byproduct buildup, simplifying the system while improving energy performance.
Sodium already has a long history in industrial-scale production. During the leaded gasoline era, manufacturers produced large volumes of sodium metal to support tetraethyllead synthesis. By the 1970s, U.S. facilities surpassed 200,000 tons annually. This legacy shows that sodium production could scale when needed. Industry also developed safe handling procedures, such as covering the metal with oil to prevent reactions with air, which simplified storage and transport.
MIT’s sodium-air fuel cell offers more than just a novel chemistry—it introduces a practical, efficient, and low-cost path toward cleaner flight. By combining abundant sodium with ambient air and turning the byproduct into a carbon-capturing asset, the design addresses energy, climate, and infrastructure challenges in a single, scalable system. While obstacles remain on the path to widespread adoption, this breakthrough position sodium-air fuel cells as a frontrunner in the race to decarbonize regional air travel and build a more sustainable aviation future.
Nicole Imeson is an engineer and writer in Calgary, Alberta.
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