A New Sodium-Air Fuel Cell Prototype May One Day Power Electric Planes And Trains

Batteries are approaching their limits in how much energy they can store relative to their weight, posing a major challenge for powering aircraft, trains, and ships. MIT researchers and collaborators have developed a promising alternative: a fuel cell that works like a battery but refuels rapidly instead of recharging.

This new design uses liquid sodium metal—an affordable, abundant material—as fuel. On the opposite side of the cell, regular air provides oxygen. Between them, a solid ceramic electrolyte lets sodium ions pass, while a porous electrode enables a chemical reaction between sodium and oxygen to generate electricity.

“Prototype Fuel Cell Outperforms Lithium-Ion Batteries by Delivering Triple the Energy Density”

In a series of tests with a prototype, the researchers showed that their fuel cell could deliver over three times the energy per unit weight compared to the lithium-ion batteries used in most electric vehicles today.

The results appear in the journal Joule, in a paper authored by MIT doctoral students Karen Sugano, Sunil Mair, and Saahir Ganti-Agrawal; materials science professor Yet-Ming Chiang; and five others.

“We expect people to think this sounds completely crazy,” says Chiang, the Kyocera Professor of Ceramics. “If they didn’t, I’d be a little disappointed—because truly revolutionary ideas usually seem that way at first.”

Chiang believes this technology truly has the potential to be transformative. In aviation—where minimizing weight is critical—dramatic gains in energy density could finally make electric flight viable on a larger scale.

“The realistic threshold for electric aviation is around 1,000 watt-hours per kilogram,” he explains. Current lithium-ion batteries in electric vehicles deliver about 300 watt-hours per kilogram, which is far below the required amount. Even reaching that 1,000 mark wouldn’t support long-haul flights, but it could make regional electric aviation—covering about 80% of domestic flights and 30% of aviation emissions—feasible.

Sodium Metal Emerges as a Promising Solution for High-Energy, Low-Cost Transport Batteries

The same high energy density and low cost requirements apply to other sectors like marine and rail transport. “That’s what drew us to sodium metal,” Chiang says.

While researchers have explored lithium-air and sodium-air batteries for decades due to their high energy potential, creating a fully rechargeable version has remained elusive.

Chiang notes, “People have long recognized the energy density promise of metal-air batteries, but despite their appeal, no one has practically realized them—until now, perhaps.”

By applying the same fundamental electrochemical principles but designing a fuel cell instead of a battery, the researchers achieved the benefits of high energy density in a more practical format. Unlike batteries, which seal materials inside for repeated use, fuel cells allow energy-carrying materials to flow in and out during operation.

Researchers Develop Two Lab-Scale Sodium-Air Fuel Cell Prototypes with Distinct Designs

The team built two versions of a lab-scale prototype. One, called an H cell, uses two vertical glass tubes connected by a horizontal section containing a solid ceramic electrolyte and a porous air electrode. Liquid sodium fills one side, while air flows through the other, supplying oxygen for the central electrochemical reaction that gradually depletes the sodium fuel.

The second version has a horizontal layout, with liquid sodium sitting in a tray of electrolyte material. The air electrode, which enables the reaction, is attached to the tray’s bottom.

When tested with air at controlled humidity levels, the system reached nearly 1,700 watt-hours per kilogram at the individual cell stack level—equivalent to over 1,000 watt-hours per kilogram at the full system scale, according to Chiang.

For aircraft use, the researchers propose inserting modular fuel packs—similar to cafeteria trays stacked in a rack—into the system. As the sodium metal in these packs reacts to produce power, it releases a byproduct, which in aircraft would be expelled like jet engine exhaust.

Read the original article on: Tech Xplore

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