- mention of a membrane. This is present in all sorts of battery technologies and tends to have weak points around cost and lifetime.

- poor passive safety. Standard lithium cells are usually tested to be puncture-safe. A tank of molten sodium cannot be puncture-safe, it will catch fire when exposed to air. So if something breaks off a plane and gets fired through the wing, the plane will become a fireball in the air.

- alkali rain. The touted benefit of being able to dump sodium hydroxide into the air omits to mention that you shouldn't get it on your skin. Yes, it will be dipersed if it's dropped from high altitude, but what about the rest of the flight?

- the chemtrail people would then be literally correct

> 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.

Remember acid rain? Now we will have alkaline rain. Using fuel for planes, that makes exhaust that dissolves the planes might not be a smart idea.

https://www.cell.com/joule/fulltext/S2542-4351(25)00143-6

Despite the claims in the article, this is hardly revolutionary in principle, but if it would work well in practice, that would indeed be a new achievement.

This sodium fuel cell combines the liquid sodium electrode and the ceramic separator of the sodium-sulfur batteries, which have been researched for many decades and which are in exploitation around the world in big installations for stationary energy storage, with an air electrode similar to what is used in the other high-temperature fuel cells. Therefore it is only a new combination of older technologies. There may be undisclosed details of the air electrode that are more revolutionary, but nothing mentioned in the article is revolutionary.

Besides the higher energy per kg, this sodium fuel cell has a second advantage over the existing sodium-sulfur batteries. It works at a lower temperature, because it is no longer constrained by the higher melting temperature of sulfur. This leads to a longer lifetime, which is currently a problem for the sodium-sulfur batteries.

Nevertheless, there are also disadvantages not mentioned in the article. While the sodium-sulfur reversible battery has a good energy efficiency for a charge-discharge cycle, this fuel cell, like all fuel cells, must have a much lower energy efficiency per the cycle of producing elemental sodium, then burning it in the fuel cell.

Moreover, producing sodium from salt is very cheap, but it also generates as a by-product dangerous chlorine gas. Some use must be found for that great amount of chlorine, otherwise storing an ever increasing quantity of it in a safe way would increase many times the cost of sodium production. The research article linked above optimistically says that perhaps the chlorine could be sold, providing additional revenue. That would almost certainly not work. The amount of produced chlorine would exceed demand, so the producer of sodium might have to pay someone to use their chlorine, otherwise the cost of chlorine storage would be even worse.

Also not mentioned clearly is that this fuel cell consumes not only sodium and air, but also water, because the incoming air must be humidified and the water is incorporated in the Na hydroxide that is the exhaust product of the fuel cell.

The optimistic energy per kilogram value does not seem to incorporate the weight of the water reservoir that will be required besides the fuel cell. The weight of the water alone will be about two thirds of the weight of sodium metal stored in the fuel cell. Therefore it appears that going from 1500 W/kg for the electrode stack alone to above 1000 W/kg for a complete device is not likely to be achieved when taking into account also the weight of the water reservoir.

This high-temperature fuel cell also requires an additional starter battery, to heat the fuel cell up to the working temperature.