New fuel cell could enable electric aviation
New fuel cell could enable electric aviation
MIT engineers developed a fuel cell that offers more than three times as much energy per pound compared to lithium-ion batteries. Powered by a reaction between sodium metal and air, the device could be lightweight enough to enable the electrification of airplanes, trucks, or ships.
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 it just me, or releasing something that creates sodium hydroxide, one of the most powerful bases over large forested areas, is a terrible idea
Im no chemical engineer from MIT, but I would assume that trace amounts of sodium hydroxide that are readily reacting into sodium bicarbonate well before they make it near the surface of the earth are probably not an issue of concern. Especially considering the acidification caused by traditional exhaust gasses
The amount of CO2 in the atmosphere is not actually very high in terms of actual percentage it represents less than half a percent so the reaction would not neutralize all the sodium hydroxide. Also trace amounts of sodium hydroxide is a bit of an overstatement if we have jetliners using 100MW while flying
What if it does that during takeoff and landing phases though.
This was my first thought as well. Both sodium hydroxide and sodium bicarbonate seem like they could have a signficant environmental impact. We'd need some good studies on that before committing to this idea, I think.
Man, when that plane makes a water landing, the real bbq starts.
No more Miracles on the Hudson, only Meltdowns.
Where exactly are they storing these fuel cells? Most commercial planes store fuel in the wings, unless I’m mistaken. Imagine a bird strike that exposes pure sodium metal to a cloud or something. Now you have a metal fire on the wing of your aircraft while it’s in flight.
But, we'll know where the aircraft is. It's a built in, instant location flare. No more aircraft disappearing and not being found.
the fuel is liquid sodium metal, an inexpensive and widely available commodity.
How very stupid we all have been during the last 200 years! /s
We don't use this "inexpensive and widely available" fuel for making a campfire, or heating a house, or driving a car.
Producing enough sodium metal to enable widespread, full-scale global implementation of this technology should be practical, since the material has been produced at large scale before.
What a bullshit again.
Let us get smarter by looking at the whole cycle of energy:
Sodium metal is used as a carrier of energy in this idea. First we would need to invest energy to create the "fuel", and later we can use the energy from it.
Now the problem gets obvious: It is not an even balance.
"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
These reactions can only be so spontaneus because there is still a whole lot of energy stored in the sodium hydroxide after the airplane is done with it. And this energy was needed in the beginning, on the way from sodium chloride to sodium metal, but later it can not be used completely for that airplane. A good part of it is wasted afterwards.
IMHO This "gap" in the cycle makes the whole idea much less useful than this guy is telling us.
Not to mention them being very blasé about dumping sodium hydroxide in the atmosphere as if there's totally no downsides to that.
Charitably, it sounds like someone highly competent in one field dramatically misjudging their competence in another: Just because you're good at chemistry doesn't meam you also know how that chemistry acts on an ecosystem.
Cynically, it sounds like someone coming up with a genius idea, hoping to make money and dismissing any shortcomings because they get in the way of money.
He's looking for dumb money
They're comparing it to lithium batteries for power density, but ignoring that the sodium metal in this case is a consumable, unlike batteries.
They say it's 1200 Wh / kg of sodium, however gasoline is a whole 3800 Wh / kg, and somehow I think the carbon dioxide is less harmful than the same amount of sodium hydroxide. Not to mention how much more complicated storing liquid sodium would be since it reacts with air.
So that might not be a big deal. Most of the energy in gasoline is released as heat and not useable.
Not sure it's enough.
Airplane engines are about 35% efficient. Maybe you can push it upwards 50% with state of the art designs.
Fuel cells hits about 60-70%, state of the art can maybe hit 85% (and the electric engines can be efficient enough to be part of the error margin in this equation). Best case you're halving wasted energy. That means you need AT LEAST half the energy density, or else you're carrying more fuel mass for the same flight. Might be tolerable if it is at least cheaper, but you're also adding stress and wear as you do.
1200 Wh / kg of sodium
That is about the H2 energy release from sodium reacting with water (perhaps just humidity in air).
however gasoline is a whole 3800 Wh / kg
H2 has 33000wh/kg, and a fuel cell gets double the energy of a combustion engine/turbine, and so if you were starting with sodium, might as well pour water on it on the ground, and fill the plane up with automatic high pressure H2.
There are no emissions other than water vapour from the sodium process because the reaction leaves solid/liquid byproducts (that are too valuable to discard) other than H2.
From what the article says, this fuel cell produces sodium oxide by reacting sodium with oxygen. There's no hydrogen gas being produced in the fuel cell.
The emissions are sodium hydroxide, or sodium carbonate after it reacts with carbon in the air.
(Also now I'm not sure where I got 1200Wh/kg from. The article says both 1000 and 1500 Wh/kg)
So it doesn't emit CO2, but it sprays drain cleaner out the back? 🤔
But that's additional value! Seriously, they Factor the price of NaOH into their cost efficiency estimation, yes, they use the retail price of NaOH to offset the sodium cost, and only by that are comparable to synthetic aviation fuel. This is beyond ridiculous.
I think probably sand blasting everything around the airport with caustic dust is possibly, a bad idea... lots of people live in the approach or departure paths... and a lot of airports sit on bodies of water, so is this like Agent Orange 2.0?
Is this better than just using hydrogen?
The trouble with hydrogen is that it is very hard to store. It's a very small molecule that can easily slip through even the tiniest gaps. So you actually have to cool it down or put it under a lot of pressure. Usually the latter is favoured because it doesn't require any energy to keep up. But it is more prone to breakage which can result in an explosion.
I think Norway ditched their hydrogen plans after a gas station exploded. Not in a Hindenburg way, "just" from the pressure.
Pressure is also bad for aviation since pressure vessels are usually heavy.
Both Boeing and Airbus are working on H2 Tech for Planes.
Depending on how they do it, not having to deal with hydrogen infrastructure might be nice, if they keep along with the plan to use refillable cartridges. Hydrogen is a bit more fiddly.
Although this seems much more reliant on humidity compared to a hydrogen fuel cell, which seems like a huge hole if the thing just won't work if it's a dry day/environment.
Considering the long term goal for them is to have them in planes at 30k ft, im sure they are entirely designed with the idea of humidifying the air to an ideal point prior to it getting to the catalyst for the reaction
Great. Use it for ocean going ships and boats. The bicarbonate will lower acidity in the water.
Best I can do is use it for small plane trips and powder the top of everything with baking soda. Side effects may include killing all plant life along common routes.
It's a red flag that they don't compare to H2, which has significant aviation FC prospects/research, and has even higher energy density by weight, and the advantage of exhausting water vapour and so fuel weight goes down during trip.
Sodium is also produced by electrolysis. It can make a lot of H2 and heat by reacting with water. In fact, the reaction of 1 ton makes 1.8mwh of heat, + 1.4mwh of H2 heat value (900kwh electric), where hot H2 might have extra energy potential for electricity or combustion (not sure).
Sodium metal costs $2000/ton. Reaction with water makes 42kg of H2, and so about $46/kg of H2 is too high. The heat would improve the efficiency of SOFCs (described matches article) by getting the heat for free, and maybe 1.2mwh/ton electric. SOFCs have always had the advantage of working with polluted fuel blends.
Perhaps if sodium or H2 production was combined with desalination process, then cost of green sodium or H2 could be lowered.
Fuck the cost. The planet is going to be unfit for human habitation in a generation or two, while ecosystems and ocean current collapse kills everything else.
All that matters is if it’s cleaner. Stop ruling out options because they’re not market friendly.
The problem is that we don’t yet have a practical alternative to jet fuel, except high speed rail and Zoom. The technologies are all too young.
And it’s not just cost, it’s trying to make them useful enough. Batteries will not take you across a continent, for any cost.
We’re more at the stage of “fuck the cost. Give me another option to try”
The real competitor for green aviation isn't hydrogen, it's bio-fuel. Bio-kerosene, bio-gas and bio-ethanol all have useful roles in aviation, and are essentially carbon neutral over their lifecycle. Zero carbon at the proverbial tailpipe is a lot less important when that tailpipe is at 30,000 feet.
bio fuels are not scalable. Much more solar energy (15x+ factor) is created by PV than by ethanol per area, and more efficiently turned into H2 (or e kerosene, btw) than the bio route. Bio route is airline PR to do something, but would make food scarce at scale.
iirc the issue with Hydrogen is that it has very high energy/mass but incredibly low density to the point that the fuel tank to contain a reasonable amount of hydrogen (say comparable to hydrocarbons) is even more prohibitive than battery weight.
300atm compressed H2 has more energy than batteries. 600wh/L electric. 900 wh/L heat. LH2 is equivalent to 1100atm compressed. LH2 is right for aviation because the tanks are light/simple, and they are filled shortly before takeoff. It's a big weight savings over kerosene.
Is it really cheaper and more practical to produce sodium vs hydrogen?
The typical issue with fuel cells is not energy density, it is the fact that you need to waste a lot of energy to regenerate and transport the fuel.
For example, if you take a classic hydrogen option, you can either get it from natural gas (which is not sustainable/eco-friendly) or from water (which is fully sustainable as you get a closed cycle, but comes with additional energy losses on electrolysis, transportation and usage).
Similarly, here with sodium you either have to produce it over and over from salt, or you'll have to regenerate soda, with the first option being wasteful and the second too energy-demanding and complicated.
So, overall, you'll need to spend much more energy (= both recurring and upfront costs) compared to running battery-powered transportation if you want to make it a close cycle similar to batteries.
Um, hold up a second. That snippet of the article said that it produces something that's commonly used as a drain cleaner. That does not sound safe. I don't particularly go around breathing drain cleaner fumes.
Continue reading.
Sodium Hydroxide, when exposed to Carbon Dioxide (already in the air), combines to become Sodium Carbinate.
NaOH + CO2 → Na2CO3 + H2O
Sodium Carbinate then reacts with water and more Carbon Dioxide to become Sodium Bicarbinate, which is baking soda.
Na2CO3 + CO2 + H2O → 2 NaHCO3
Not only does a Sodium Oxyde fuel cell produce electricity, it takes CO2 out of the atmosphere.
From a physics and chemistry point of view, it's pretty cool. I'm curious how well it scales though.
It still might be problematic around airports if people on the ground breathe it in before it reacts. And what about all the sodium bicarbonate precipitating all over the ground? That's bound to affect the local environment before it ends up in the oceans..
That said who knows maybe it's better than the carbon dioxide alternative
So here comes alkaline rain to replace the acid rain we got rid of 40 years ago. Genius idea. Not
And, hey, good luck with it.
Uh, how are those trains coming?
Same thing as a diesel electric train
I wonder if that takes an appreciable amount of carbon out of the air, and if it is somehow persisted in solid form.
I love the fact that they just gloss over the fact that all the sodium will FUCKING EXPLODE if you even get so much as a crack in one of your fuel containers or the battery or any kind of leak in the connections etc. Definitely not keen to be on an airplane with that on board!