Researchers at MIT have developed a low cost fuel cell that, in tests, has proved able to carry there times as much energy as a lithium-ion battery, a potentially seismic development for electric transport.
Lithium-ion batteries as used in electric cars can’t store enough energy for long-range, heavy-duty vehicles like planes, ships, and trains. But a potential solution might have been found in a new kind of fuel cell powered by liquid sodium, a cheap and abundant material.
An H-cell modified with electrodes and an ion-conducting ceramic membrane to conduct sodium-air fuel cell experiments.
The fuel cell works differently from a traditional battery. Instead of needing to recharge, it can be quickly refueled, like filling a petrol tank. On one side, it uses liquid sodium metal as the fuel.
On the other, it uses ordinary air for oxygen. Between them sits a ceramic layer that helps the chemical reaction happen. When sodium reacts with oxygen, it produces electricity, and the byproducts are captured safely.
In lab tests, this new system delivered over three times the energy per kilogram than the lithium-ion batteries used in electric vehicles today. That’s a big deal, especially for aviation, where every kilogram matters.
While lithium-ion batteries have an energy density of between 200-300 watt-hours per kilogram (Wh/kg), MIT were achieving over 1,000Wh/kg – not enough to support long-haul flights but a potential game-changer for regional aviation.
The technology will also be attractive to other modes of transport in which high energy density is required, such as trucks, ships and trains.
Professor of materials science and engineering Yet-Ming Chiang explains: ‘They all require very high energy density, and they all require low cost. And that’s what attracted us to sodium metal.
‘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 realised in practice.’
If this weren’t enough, the byproducts of the reaction would actively remove CO2 from the atmosphere, effectively producing a climate-friendly exhaust. When sodium reacts in the air, it forms compounds like sodium hydroxide and sodium bicarbonate, which can capture and lock away CO2.
This system also comes with safety advantages. Unlike traditional batteries that store energy in a closed space – which can lead to fires or explosions – this fuel cell keeps the sodium and oxygen separate, lowering the risk of runaway reactions.
Although the device is currently just a small lab prototype, the researchers have started a company, Propel Aero, to bring the technology to market. Their first goal is to create a fuel cell the size of a brick, powerful enough to fly a large drone.
Because sodium is plentiful and easy to extract from salt, scaling up production is feasible. The researchers envision a system where refillable sodium cartridges could be swapped out and refilled, just like changing propane tanks.
Chiang added: ‘We expect people to think that this is a totally crazy idea. 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.’
The full research can be read here.
Photo: Gretchen Ertl
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