Instead of a battery, the new concept is a kind of fuel cell — which is similar to a battery but can be quickly refueled rather than recharged. In this case, the fuel is liquid sodium metal, an inexpensive and widely available commodity. The other side of the cell is just ordinary air, which serves as a source of oxygen atoms. In between, a layer of solid ceramic material serves as the electrolyte, allowing sodium ions to pass freely through, and a porous air-facing electrode helps the sodium to chemically react with oxygen and produce electricity.
In a series of experiments with a prototype device, the researchers demonstrated that this cell could carry more than three times as much energy per unit of weight as the lithium-ion batteries used in virtually all electric vehicles today.
A great deal of research has gone into developing lithium-air or sodium-air batteries over the last three decades, but it has been hard to make them fully rechargeable. “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.
By using the same basic electrochemical concept, only making it a fuel cell instead of a battery, the researchers were able to get the advantages of the high energy density in a practical form. Unlike a battery, whose materials are assembled once and sealed in a container, with a fuel cell the energy-carrying materials go in and out.
The researchers envision that to use this system in an aircraft, fuel packs containing stacks of cells, like racks of food trays in a cafeteria, would be inserted into the fuel cells; the sodium metal inside these packs gets chemically transformed as it provides the power. A stream of its chemical byproduct is given off, and in the case of aircraft this would be emitted out the back, not unlike the exhaust from a jet engine.
But there’s a very big difference: There would be no carbon dioxide emissions. Instead the emissions, consisting of sodium oxide, would actually soak up carbon dioxide from the atmosphere. This compound would quickly combine with moisture in the air to make sodium hydroxide — a material commonly used as a drain cleaner — which readily combines with carbon dioxide to form a solid material, sodium carbonate, which in turn forms sodium bicarbonate, otherwise known as baking soda.
“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.”
As an added benefit, if the final product, the sodium bicarbonate, ends up in the ocean, it could help to de-acidify the water, countering another of the damaging effects of greenhouse gases.
Initially, the plan is to produce a brick-sized fuel cell that can deliver about 1,000 watt-hours of energy, enough to power a large drone, in order to prove the concept in a practical form that could be used for agriculture, for example. The team hopes to have such a demonstration ready within the next year
Is this better than just using hydrogen?
Where do you get the H2 from?
Electrolysis? Ideally from excess solar or nuclear.
Best case, but a lot of hydrogen is produced using fossil fuels by my understanding.
Sufficient storage capacity to meet overnight needs is going to be a challenge; storage to meet seasonal production variation is impossible. To make solar feasible, we need to build out sufficient generation capacity to meet our needs in winter. Winter, with, perhaps, 9-hours of mostly overcast skies and low angles over the horizon.
Imagine the output of that same system in summer: 15 hours of high-angle daylight and mostly clear skies. The summer output of that facility will be at least 400% its winter productions.
The solar economy needs absurdly massive electrical loads in summer that can be readily shed over winter. We may see fleets of factory ships, loaded with electrolysis equipment, plugging into grids on whichever side of the equator is currently experiencing summer.
Maybe one day but for now it's just green washed big oil
The technology plans for these fuel cells aren't "for now". They're for a future where we've hopefully already decarbonized most of the electric grid, as doing so is way more important than decarbonizing aviation. Converting fleets of airplanes to electric is a long process that will probably not be started for a while yet while there are more important carbon emission sources to tackle (aviation is only 2-3% of the emissions right now).