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Powerpaste, a hydrogen technology for small vehicles (fraunhofer.de)
167 points by apsec112 11 months ago | hide | past | favorite | 96 comments

Solving hydrogen storage has great implications. Hydrogen has high gravimetric energy density (1 kWh worth of H2 is light) but very low volumetric density (1 kWh takes up a large volume). Easy solutions are compressed hydrogen (H2 is a small molecule and easily escapes even through a material, steel embrittlement and energy for compression are big issues), cryogenic cooling (energy intensive and cryocoolers have significant capex) and metal hydrids. To put it simply the crystalic structure of the metal acts as a high pressure storage tank. H2 is typically released by heating the material up.

One thing they didn’t mention is energy used for round trip per unit of H2 and cost of the material itself. Neither was discussed there. Many similar materials exist already.

Many CO2 neutral pathways with other molecules exist. Amonia, methanol, ethanol, DME, urea, formic accid and so on.

PS: If you’re into this stuff, keep an eye on the Fraunhoffer institude. They have many cool projects. (I am not affiliated with them in any way)

> One thing they didn’t mention is energy used for round trip per unit of H2 and cost of the material itself.

I also did not see anything about recycling the carrier materials which seems suspiciously odd in a context so closely related to environmentalism.

But the big picture news is that this is another datapoint that shows how, like you said, the solution space for what I like to call "bound hydrogen" is apparently not exhausted at all yet. In recent months I have seen (all on hn) power-to-ammonia, that Dutch group that proposes iron powder as a heat fuel of roughly coal performance that is recycled by reducing the returned iron oxide powder with hydrogen (and started to fuel a brewery as a pilot) and now this "powerpaste" which sound like straight out of the back to the future future. The claimed energy density is absolutely amazing! If the required infrastructure hardware is small enough it could be a gamechanger for BEV: size the battery to be sufficient for 80% of driving days and install the "1000 miles extra" block where it can be accessed for replacing, e.g. where an ICE car would have it's engine. Chances are the extra miles fuel won't be cheap, but you'll surely be able to buy a lot of RX refills for the battery cost saved if a strong majority majority of your driving can be done on battery only.

I always considered the term "hydrogen economy" silly because of how annoying H2 is to deal with at scale, but "bound hydrogen" can change that in so many ways. It's almost as if hindsight was trying to win a bet or something wrt how we look back at George W. Bush, first him appearing so unexpectedly presidential compared to a certain successor, then suddenly hydrogen economy ceases to be a joke. What's next, discovery of actual WMD so they could have well stayed honest had they just looked a little harder? Harris becoming president after "pretzel incident 2"? Bound hydrogen is the most exciting technology field since many years.

Bound hydrogen is what is in gasoline and any other hydrocarbons. So it is nothing new, but a method for storing energy already used for a few billions of years, since free dioxygen appeared on Earth.

The only chemical substances that can approach hydrocarbons in energy density must be composed of light elements, preferably able to lose many electrons by oxidation.

So aluminum hydride would be better from this point of view than the magnesium hydride and ammonia is a very good solution if it is desired to avoid making hydrocarbons from carbon dioxide.

Nevertheless, nothing practically usable beats hydrocarbons in energy density. However it is unknown yet whether another form of storage, e.g. ammonia or another hydride a.k.a. "bound hydrogen", would not be better for the efficiency of a complete cycle of storing the energy by chemical synthesis, then recovering it using a fuel cell or a thermal engine.

> "The claimed energy density is absolutely amazing!"

Specific energy of magnesium hydride is 7.7% of H2. Energy density by volume is 13.3 MJ/L, about 40% that of gasoline. The fuel cell should be more efficient than an internal combustion engine, however, so you probably make back the difference.

Well, I don't think hydrogen is the answer for all these reasons. It seems, that sodium (Na) can under certain conditions (very thin film, e.g. when applied to a surface with great speed of 10s of m/s) react directly with water and produce stable electric current. That is not so hard to do, e.g. hard disks, regular turbines etc. pretty much would provide such conditions :-) The patents for such use in Lockheed-Martin rockets expired long ago but it seems based on the details, that it worked reasonably well.

Sodium is very easy to handle. There is no need for large pressure or any bonding elements. The hydroxide can be turned into sodium again by well known processes that were used on industrial scale more than 100 years ago already. This process and the "burn" of sodium with water both release hydrogen as a by-product. This could solve the winter energy storage issue. Also you could quite likely safely transport sodium in former oil tankers or by pipe if heated to a bit more than 100 °C/ or in the form of concentrated hydroxide (the "waste")... so the infrastructure is mostly there. As you all well know, original sodium can be extracted from regular NaCl salt that we have plenty of in sea water and salt mines.

Best of all, sodium reacts so rapidly, it could under minor adjustments replace diesel in +- regular engines too. (That is also the contents of one of the patents.) That is of course not so efficient, but there is a large installed base.

> Sodium is very easy to handle.

It only blows up when it touches water.

From an engineering point of view, that might still count as easy. Especially compared to hydrogen.

You can carry gasoline in an open pail, spill it all over yourself, and even throw a lit cigarette right in the pail, all without harm, all while having very high energy density.

Sodium is not remotely in that class.

If we were to use sodium on such massive scale, I'm wondering what we would do with all the chlorine.

Doesn't most of what you said also apply to magnesium? Seems like we'll never run out (2.5% of earth's crust), there are well established methods to refine it and you just react the hydride with water to generate hydrogen.

Hehe never run out. Like we never ran out of IPv4 addresses or crude oil... I think any solution needs to be cyclic.

Looks like there is ~10^−8 earth masses of oil and coal [1]. I can't seem to find the mass of magneisum on earth but its 2.5% of the earth's crust, which is apparently <1% of the earth's volume, lets estimate 0.1% of the total mass to be conservative, not sure how reasonable this is but seems ok for this back of the envelope calculation [2]. This gives about ~10^-5 earth masses of magnesium, still orders of magnitude more than the oil and coal and this process won't consume it, its just for hydrogen storage/transport.

More numbers on the mass of the crust in [3].

[1] https://osf.io/dkmwy/download [2] https://en.wikipedia.org/wiki/Earth%27s_crust [3] ttps://ui.adsabs.harvard.edu/abs/2007AGUFM.V33A1161P/abstract

This magnesium hydride technology certainly does not solve the hydrogen storage problem in the sense of being better than using hydrocarbons for energy storage, as the living beings have been doing for billions of years.

For many applications, using magnesium hydride should be much better than using compressed or liquefied hydrogen, but it remains far worse than gasoline despite the misleading statement from the article "POWERPASTE offers a range comparable to – or even greater than – gasoline".

This statement is false. Magnesium has twice the atomic weight of carbon and the hydrogen from magnesium dihydride provides only 2 electrons per magnesium atom, instead of 6 electrons per carbon atom, as in gasoline.

Because of that, a fuel cell using hydrocarbons (those exist, but the current prototypes do not have an acceptable lifetime) would have a 6-times higher energy capacity per fuel weight.

While the energy per weight of magnesium dihydride is very poor, the energy per volume is more decent, because gasoline has low density.

Nevertheless MgH2 has only twice the density of gasoline, which means that the hydrogen content per volume is about the same as for gasoline. Because when used in a fuel cell gasoline would provide 3 times more current per volume, magnesium hydride remains uncompetitive regardless how the storage cost is computed.

Pure dihydrogen would provide a voltage around 20% higher than hydrocarbons in a fuel cell. That is much too little to make a difference compared to factors of 6 and 3 in current per weight and current per volume.

Instead of wasting time and money to search for impossible ways of storing hydrogen, the energy research should be directed to improving the (already existing) technologies for making hydrocarbons from carbon dioxide and for making hydrocarbon-using fuel cells with better characteristics.

Are you seriously suggesting we should waste our renewables and nuclear to capture CO2 from the atmosphere and then turn that stuff back into hydrocarbon fuels only to turn 80% of it to waste heat?

Seriously, man. There is no future where this is going to happen. We are not going to replace waste primary energy generated by fossil fuels by wasting our low carbon energy. We are going to reduce the amount of waste energy and thus lower the overall demand for primary energy. The energy density of gasoline is worthless if the efficiency is garbage.

A transition from ICEs to EVs works just fine without expanding power generation significantly precisely because we get rid of the inefficiency.

You are right that the main disadvantage of storing energy in hydrocarbons is the low efficiency of the complete cycle, which is indeed around 20% today.

It is likely that the efficiency can be improved a lot but it is improbable that the efficiency of the complete cycle could reach much above 50% any time soon.

So you are right, for the best efficiency rechargeable batteries are the best.

Nevertheless, there are many cases when a maximum autonomy time is more important than the efficiency, together with the possibility of storing the energy for an indefinite time without any losses (e.g. due to self-discharge). In those cases hydrocarbons are optimal.

So both technologies are necessary and each has uses for which it is the best.

For example, a healthy human can live about one month without eating, due to the stored hydrocarbons, i.e. fat.

No future robot using lithium batteries will be able to do that, while performing a similar activity level and having the size of a human.

> It is likely that the efficiency can be improved a lot

What makes you think that? I thought internal combustion engine efficiency is widely believed to have hit its reasonable limits?

Internal combustion, or any form of combustion, is only one way to get energy back out of a hydrocarbon.

And a hydrocarbon cycle doesn't necessarily have to be all that efficient to be practical, if the primary energy input is renewable, and the cycle is largely closed (IE, a plant somewhere consumes the same stuff the vehicle produces). The portability, safety, ease of handling, and rapid simple refill of hydrocarbons outweighs a lot of other factors at the point of use for some jobs, mainly vehicles.

Most other energy-consuming jobs can use a wide variety of other forms of energy, so this is mostly about vehicles, not energy usage in general. This is why your furnace doesn't burn gasoline.

Anyway what they're saying is that entire cycle can probably be improved a lot from what we can manage today.

We can surely continue discovering new and better ways to make a fuel cell that consumes a hydrocarbon.

And we are definitely still discovering a variety of different ways to synthesize hydrocarbons. Some have a lot of overhead like planting corn and eventually getting a small quantity of a low-density hydrocarbon (alcohol).

Some are more direct bulk inustrial processes that are fairly cyclic and lower overhead than farming.

We already have a variety of examples of both the consumer and generator parts of the cycle and we are definitely not done discovering all the possibilities.

It wouldn’t be a permanent solution but there are trillions of dollars worth of infrastructure built around petroleum fuels. Moving personal vehicles and metro transit to EVs is straightforward, but it’s less so for freight/marine/aircraft and doesn’t account at all for industrial uses of petroleum fuels.

TIL you can put gas in a fuel cell. Why don't we today? That seems like a handy way to run a hybrid

You don't need hydrogen, you need electrons. I prefer to store my electrons directly in atomic element 3, so I can fill it directly with electrons and get them back out, at much higher efficiencies than this process.

In all energy storage tech, you're trading off energy density (eg. energy per kilogram) against power rating (energy per second that you can transfer). Then you have trade-off considerations like safety, emissions (which have a value - see Tesla P/L), production cost, supply chain etc. For different use cases, different trade-offs may work out.

Lithium battery tech typically trades off power rating and energydensity (Earlier - how much acceleration and range, nowadays with better batteries - how fast you can fill up) for other benefits.

This tech prioritises safety and power rating at some production cost and supply chain.

Gasoline gives emissions and engine complexity vs other conveniences

Rockets prioritize both power and energy density over everything else and uses LH2 and LOX dealing with cryo complexity

Ion engines are another interesting technology. They are almost the opposite of rockets: very low power and very low force, but great energy density.

Keep in mind that both rockets and ion engines actually have fairly low realized energy density, because they can't just rely on atmospheric oxygen.

Unless you're thinking of a hybrid supercapacitor, you're still going to need a chemical reaction first.

In '99, while working at a solar hydrogen startup as a recent grad, I was exposed to a fellow who proposed to transport H in the form of H2O, and his solution for cracking it was to make purple ping pong balls filled w/ Na. He'd deliver a hopper of Na ping pong balls, and a machine filled with water. Feed balls into the machine, which would then use a ram to split the balls underwater, and siphon off the resulting H2 gas to feed to your fuel cell.

The racket it made, with a loud kerchunk splitting the balls, and the hissing immediately following, was just slightly terrifying.

This paste seems a good deal saner in comparison.

Not that internal combustion engines are the model to aspire to... but they're just a metal contraption full of explosions. Being terrifying isn't necessarily a disqualifier, haha.

Full of combustions, not explosions.

“The speed of the reaction is what distinguishes an explosive reaction from an ordinary combustion reaction.” - Wikipedia on explosion.

“An internal combustion engine nominally operates on a controlled rapid burn.” - WP on combustion.

Internal combustion engines do in fact attempt to burn fuel and oxidizer at maximum stoichiometric efficiency, and they also are trying to burn it as quickly as possible to capture all of the heat rather than exhausting a partially burnt mixture and wasting fuel.

Effective explosives have the exact same chemical goals and nearly the same thermodynamic goals.

If that isn’t a carefully controlled explosion I don’t know what is. I mean, come on, a piston moving up and down thousands of times per minute isn’t explosive enough for ya?

Engines combustion is designed to occur as a propagating flame front in the cylinder initiated by the spark plug. Great efforts are made to ensure that this is precisely what happens.

The alternative is a detonation, i.e. engine knocking. This causes a spike in cylinder pressure and will quickly destroy an engine. It is for this reason that engines are absolutely not trying to burn fuel as quickly as possible.

This is a difference of detonation vs. deflagration. Whether you consider both of these to be forms of explosions is a semantic issue.

> ...trying to burn it as quickly as possible...

No, the speed of burn in an internal combustion engine is not explosive:

“Knocking (also knock, detonation, spark knock, pinging or pinking) in spark ignition internal combustion engines occurs when combustion of some of the air/fuel mixture in the cylinder does not result from propagation of the flame front ignited by the spark plug, but one or more pockets of air/fuel mixture explode outside the envelope of the normal combustion front.” - WP on engine knocking, which is undesirable and may damage the engine.

Sounds to me that the problem is not the speed of the explosion that happens when engine knocking, but the timing of it.

There are HCCI engine prototypes, but they are finicky, because the mixture (mostly regarding initial temperature and pressure) has to be in a narrow flammability band, so that it ignites precisely at Top Dead Centre from adiabatic compression heat.

If it ignites earlier, the pressures are far higher than normal. If it doesn't trigger, it won't for the complete cycle, as the piston expands and the temperature drops.

Free-piston engines have an advantage there, as they don't force the compression ratio with a crankshaft. They would decelerate the piston somewhat earlier and harder than necessary, but there are no bearings that have to handle this load.

Their issue has more to do with extracting energy from the oscillation, and keeping a stable operating point that's neither prone to stalling nor prone to runaway.

> Full of combustions, not explosions.

It's both, no? Aren't all chemical-based explosions considered combustion?

If "explosion" means "a violent release of energy", that seems a reasonable word to describe what happens in a cylinder in about ~5 ms.

Explosion is a faster speed of burn than what an internal combustion engine is designed for.

Yes. And for another example: gunpowder is not considered an explosive.

In fact, only half of the hydrogen originates from the POWERPASTE; the rest comes from the added water.

Indeed, it seems it's an hybrid of your fellow's tech, using magnesium both as a substrate for H2 and as a reducing agent for water: Mg + 2H2O -> Mg(OH)2(aq) + H2(g)

Less explosive than Na, hopefully :)

Reminds me of my undergraduate days in the 1980's, when the chemistry majors' idea of fun was stealing chunks of sodium from a lab and throwing them off a bridge into a nearby river.


I had a high school science teacher who was demonstrating controlled burning of sodium and potassium one day by slicing of pieces from a large sample. Being covered in oil, the main chunk got away from him and dropped into the lab sink which was unfortunately wet from previous cleaning. A vigorous reaction ensued :)

There was another group during that era doing something similar with sodium hydroxide, which is a little less... violent. Not quite sure I recall how that chemistry worked, but I think the idea is 'find something where the hydrogen bonds are easier to crack than H2O'.

Now there are other groups trying to figure out if they can increase the power capacity of batteries by replacing the electrolyte. Which sounds like a fuel cell/battery hybrid to me.

Aluminum oxidation.

It would be lot easier to just use sodium directly and have hydrogen as a by-product. (See my other comment.)

If you're going to use metallic sodium as energy storage you might as well use it directly in a battery.

Storage of hydrogen in a solid has come around a few times already.

University of New South Wales. (2020) [1]

Lawerence Livermore Lab (2018) [2]

University of Salford (2006) [3]

Older approaches involved lithium hydride chips. Not ICs, just chips of metal. The University of New South Wales system used titanium and other secret ingredients. That one is being offered as a product for stationary storage, Real Soon Now.[4] Original article said it would ship by the end of 2020, but it has slipped to June 2021. You can pre-order the "launch edition" now. It's not a Kickstarter, but it's close.

Unclear if this is a good idea, or the next Bloom Energy Server.

[1] https://www.smh.com.au/environment/climate-change/alchemy-of...

[2] https://str.llnl.gov/2018-01/wood

[3] http://usir.salford.ac.uk/id/eprint/16768/5/Hydrogen_storage...

[4] https://lavo.com.au

What's wrong with Bloom Energy Servers?

> Onboard the vehicle, the POWERPASTE is released from a cartridge by means of a plunger. When water is added from an onboard tank, the ensuing reaction generates hydrogen gas in a quantity dynamically adjusted to the actual requirements of the fuel cell. In fact, only half of the hydrogen originates from the POWERPASTE; the rest comes from the added water

OK sounds great! so this stuff is more sensitive to moisture than LiPo batteries and yet has to be dispensed somehow; that's going to be fun.

I'd like to see the reaction, here... We talking a little steam or dropping sodium chunks into a pond?

Sodium is boring. Potassium is much better!

Seriously, though, this sounds like a horrible technology. Synthesize fancy goo that is unstable when wet. React with water to make hydrogen (itself moderately dangerous). Produce some kind of slush containing magnesium hydroxide (presumably) and miscellaneous organic crud as waste. What, exactly, happens with the waste?

At least magnesium hydroxide is not as nasty as sodium or potassium hydroxide, but you still don’t want to get it on your skin if you can avoid it.

It's not like petroleum is all that nice though, it's just that the handling around it has been pretty much perfected over the decades. You can collect spent sludge at the same place a scooter has to come anyway to refill and then re-hydrogenate the sludge into fresh paste.

The big difference, of course, is that petroleum doesn't explode or combust when rained on. Aside from sparks or ignition sources, it can sit in a bucket or puddle and be happy staying put.

Neither does this substance though. It releases hydrogen when in contact with water, not explode or combust. It might, of course, explode if sparks are introduced but the same thing can happen to hydrocarbon based fuels.

In any case, what a substance does when rained on is not very relevant for a fuel that is kept in a fuel tank at all times. By the time it's exposed to the weather, the vehicle must have crashed and in such a circumstance most safety guarantees are out of the window anyway.

No hydrocarbon fuels aren't oxygenated. Put a spark plug in your gas tank, run it day and night - nothing. Has to be oxygen in there.

The same happens in a pure hydrogen atmosphere? Not sure what you are trying to convey here.

Sorry, that comment about a spark being a problem prompted my comment. I must have misunderstood.

"miscellaneous organic crud" i figure you would recycle all of it in an environment where the slurry is saturated with hydrogen gas at high temperature and pressure, and what happens is the water reacts to make magnesium oxide, back to hydride

In 2005 there was similar hype around efficiently storing hydrogen, but using ammonia. Can't find any sources on why that didn't go anywhere though.


Ammonia is currently considered as one of the more promising options for future shipping fuels.

There are a number of projects planning to create green ammonia at scale, e.g. this: https://asianrehub.com/

Ammonia is already made from hydrogen today, making that green is pretty straightforward, you just need enough clean electricity. Just get the hydrogen from electrolysis, the ammonia synthesis process itself is well established technology.

Ammonia is one of the less pleasant chemicals one could use. I'd rather have Hydrogen-exuding paste than Ammonia in an accident. The Hydrogen might explode. But the Ammonia definitely will hurt you.

Ammonia is quite ok. You can smell it :-) You can put it into water, where it is quite stable. We know how to handle it at industrial scale because of fertilizers.

Yes, you can smell it, when drastically diluted in water (which, as you say, is stable) such as for a household cleaner. But in a concentrated form such as that required for use as fuel, if you smell it, it will kill you. Quickly.

Also, water-free Ammonia is gaseous at room temperature, you have to transport it in pressurized containers. Should one of those rupture, all the Ammonia will boil off, creating a nice cloud of fun for all involved. Neutralizing it works by spraying acetic or hydrochloric acid, which is not quite as bad, but still quite ugly.

Why not just use a closed loop hydrocarbon from electricity system as a shipping fuel if you have excess power and a need for transit?

The main theoretical point of hydrogen is very high specific energy per mass but it is essentially purest acidic gas and a pain. Bonding it to something else mitigates it so why 3 H per N instead of 4 H per C? Both are toxic gases at this point leaving ammonia's main advantage in the context being its own oderant.

The problem with every hydrocarbon-based fuel is that you need the carbon.

You get that from CO2. But then you need to get the CO2. Where do you get it from? From a fossil-based plant? Well, ideally you'd want to get rid of those, not exactly smart to create incentives to keep them running. The alternative is either biomass (problematic) or direct air capture (expensive and inefficient). (Some insightful discussion on green methanol: https://www.youtube.com/watch?v=jXACyUxxBts )

With non-carbon based fuels like hydrogen or ammonia you skip that problem (air is 78% nitrogen, much easier to extract).

or direct air capture (expensive and inefficient)

The big question in my mind is whether direct air capture is inherently expensive and inefficient...or if this is just a chicken/egg problem where we haven't invested time and money in making it cheaper because it's expensive, and it's expensive because we haven't invested time and money in making it cheaper.

I don't know enough about physics and chemistry to answer the question on what the theoretical lower bound on cost might be.

From some research into the feasibility of an indoor CO2 scrubber that targets pre-industrial concentrations (100~200 ppm), using a sodium hydroxide solution in a simple counter- or cross-flow packed-bed wet scrubber does a good job at scavenging CO2 from the air down to <100 ppm on the exhaust, while the hygroscopic sodium hydroxide has an equilibrium with ambient humidity at all relevant indoor living room temperatures and humidities.

Regeneration is easy in another counter-flow packed bed reactor, this time reacting with a CaOH bed to exchange the carbonate ion. The output is mostly CaCO3, with some NaOH contamination. This can probably be washed for home-scale disposal (and recuperation of the NaOH), while the industrial scale process follows up with thermally decomposing the CaC03 into CaO and CO2. This can be very pure CO2 suitable for direct sequestration, if the thermal energy is provided electrically or by combusting a hydrocarbon with purified oxygen.

So the lower cost would seem to be that of calcinating the limestone (at 900~1050°C), and a trade-off between cap-ex and op-ex for the scrubbers. The lower the flow rate, the less energy is needed to force the solution and air through the packed bed.

But afaik freezing the CO2 out of the exhaust from fossil fuel power plants and industrial processes requires less energy than the calcination, and is therefore economically favored until all easy opportunities have been converted.

The calcination seems to require about 800 Wh/kg of CO2. At typical electricity rates in favorable locations of 10 ct/kWh, this makes 1 kg DAC-CO2 cost >~8 ct. If you want the carbon out of this, you're looking at 1.25 $/kg of DAC carbon. Assuming perfect electrolyzation of the CO2.

It's inherently expensive, because you have to undo the entropy loss of letting the CO2 diffuse into the atmosphere. It basically means running an expensive molecule sorting operation, whose cost has a floor set by the laws of thermodynamics, in advance of whatever else you wanted to do with the CO2.

That entropy loss is not that large (it's logarithmic in the dilution). A bigger problem is simply the cost of handling a lot of air.

Direct air capture is inherently expensive unless you are doing it in the airstream of some industrial process that produces large amounts of CO2, and even then its still somewhat expensive.

Even as a waste product from separating Nitrogen, Oxygen and Argon from the air, its still expensive (retail its ~$1/lb of liquid CO2).

> The big question in my mind is whether direct air capture is inherently expensive

Have a look at a tree...

I suppose it's possible that billon years of evolution has ended on a local optimum for low energy input (direct sunlight), and we might revolutionize it with high energy (eg: high voltage electricity, fusion etc) - but I doubt it.

> low energy input (direct sunlight)

Direct sunlight is actually quite powerful, around 1kW/m^2 at sea level.

Although I'd guess most trees aren't particularly efficient at absorbing CO2 vs the energy they consume, which makes sense, since they only have to be as efficient as necessary to survive.

2% efficient, at best. 1000J in, 20J worth of wood and leaves out. Burning it, you get back only a fraction of that, with much of it carried away in the smoke.

That sounds about right. It takes a whole lot of energy to reverse entropy at the margins. Then again life exists basically at the margins of the massive energy output of the sun.

But still, I'm not holding out that any such human created sunlight to chemical energy storage process is going to best the 20% conversion efficiency of solar panels * 95% round trip efficiency of modern batteries any time soon.

I know there are companies trying to make synthetic fuels from atmospheric C02 + renewable electricity for very specific use cases that are challenging for batteries (i.e aviation) but the jury is still out on whether that will work at scale.

I here predict that there will not be any producers of fuel from atmospheric CO2.

The prices of extracted petroleum and CH4 will plummet as carbon taxes increase and demand decreases, until only the absolute cheapest extractors remain, and those products will be used only where the carbon tax can be afforded: mainly aircraft, and then only until the much more cost-effective LH2-powered airframes ground them. (Those will be fueled with LH2 generated on the spot at airports using regional solar.)

Solar-powered CO2 capture projects will bid for carbon tax credits. Only the cheapest processes will win bids, so will not produce fuel. Probably they will blow it underground, in places where the ground is porous, and let it react with rocks down there. Turning it into fuel and selling it will not qualify as reclaiming, because the carbon doesn't stay claimed.

It seems pretty obvious that extracting a gas that is less than a tenth of a percent in the air is inherently difficult.

That said: I'm all for investing in DAC technology. We will definitely need it for some sectors. But you need to consider the costs and if there are alternatives they will in many cases make more sense.

We need to deploy direct air capture of some form anyway because we're not reducing our carbon output quickly enough.

According to Wikipedia, CH4 is actually non-toxic (which is what I'd expect for something so ubiquitous in biological systems).

Used to work at the Leibniz institute in Dresden, near where this research at the Fraunhofer institute on POWERPASTE is happening.

Not sure why they are trying to brand in all caps, but highly recommend adding Dresden to your bucket list post Covid. Most beautiful city I have experienced.

... and all built since 1945, an as-exact-as-possible copy of the city that had previously existed, in the same place, in 1943. It took decades of devoted work by thousands of people who loved their city, and needed to realize it again before they took their memories to the grave.

I know this sounds awfully complicated to handle (and recharge), but I think the market for practical applications of H fuel is existing, so these ideas can be evaluated in practice.

Also, not every invention has to save the world. So this paste might become useful for drones or in spacecraft. Depending on the energy density it might even be very usable for electrified air travel.

If storage losses are sufficiently low and the converter hardware is small/cheap enough maybe the process could also find a market as a sealed system, a factory-recyclable single use battery. How about a 3HU rack form factor that if installed in groups automatically coordinates depletion to oldest-first? Main market would be what is currently served by rarely refueled backup generators but it could have a huge long tail of undiscovered use cases wherever power density of batteries is insufficient and diesel generators suffer from noise or bad maintenance, but where fuel price isn't the main concern. Pricing model could be as easy as implementing effectively fuel + rent with a deposit that shrinks over time (blockchain the device log if it makes you feel better somehow). Once established for server rooms, fishing cabins and whatever other niche it will find it might even end up mainstream with BEV that opt for just offering an RX rack over killing range anxiety with half a ton of extra rechargeable that is never really needed. Approaches like this are usually made impossible by chicken/egg problems, but if it starts in a niche both technology and distribution can grow organically. Remember how Tesla was "the laptop battery car" while incumbents insisted on starting all their BEV projects (they did exist) by reinventing the battery?

I'm trying and failing to come up with a use case where this is more practical than a rechargeable (and/or swappable) battery in a scooter.

Refueling something like this would be faster than recharging, but if "quick recharge" is part of your requirements then it's straightforward to make a scooter battery swappable and maybe even standardized across brands.

Power outlets are ubiquitous, and these things just don't use enough energy to be more than a rounding error on anyone's electric bill (100 (scooter) km worth of energy is roughly the difference between washing your hands in hot water instead of cold water for 30 seconds).

There might a weight savings but lithium ion is something like 60 grams per kilometer of range for a light, slow vehicle. So a reasonable range battery is not prohibitively heavy even for a vehicle that you have to carry.

I'm sure there's a use case for this stuff, and scooters are trendy right now, but I don't think the two are a good match.

From the article, one other use case are drones, in which case even minor weight savings can be extremely valuable.

What is a scooter? A skateboard with a handle or a small motor bike? I suspect Fraunhofer is talking about the latter, and you the former.

Based on the article and some guesses, potential advantages to swappable batteries might be: weight (as you mention); cheaper/more environmentally friendly materials; lower risk of spontaneous combustion; less dangerous stuff leaking out when the unit is breached.

LFP is as safe as it comes, and the density is hitting sweet spot for scooeter distances.

Ah chemistry is pretty neat. Presumably there is a process to take the left over magnesium hydroxide and convert it back into metallic magnesium? Their explainer[1] doesn't say much about that part of the process. (note it looks like you can bake it at 332 degree C to get magnesium oxide. (can you tell I'm not a chemist?) I think it would be helpful to have the entire fuel cycle laid out somewhere.

That said, the operational infrastructure requirements for this seem to be much easier to satisfy with off the shelf technology than hydrogen storage which, frankly, is really really hard.

[1] https://www.zess.fraunhofer.de/content/dam/ikts/zess/documen...

There are a few industrial processes used to convert magnesium oxide to metal, for example the Pidgeon process (https://en.wikipedia.org/wiki/Pidgeon_process) which I still remember learning about in my Materials Science undergrad in Toronto.

More info here: https://en.wikipedia.org/wiki/Magnesium

I suspect some variation of these processes could convert the spent fuel back to metal and then the hydride form or something like that.

Thank you. That is excellent information. I wonder if anyone has looked into concentrated solar as the heat source for small batch magnesium production using that method.

Appears so: https://www.sciencedirect.com/science/article/abs/pii/S09596...

Although, looks like much of this is done with hydroelectric processes (same with Aluminum production).

Nice! And yikes! "Mg recovery in the outlet products was identified as one of the most critical process challenges because of the pyrophoric property of the produced nanopowder and its strong oxidation reactivity with air."

Seems like it would be easier to accomplish in batch processing where you could cool to a point where you were under the activation energy of the magnesium reaction with air.

But the really awesome thing is that one could set up fuel reprocessing facilities in unused areas with high solar flux (aka deserts) and transport the resulting magnesium back to be made into paste again.

And the reason that is cool, is because one of the challenges with solar power is that electrical transmission wastes energy and storage is finite. Storing energy in chemical bonds like plants do is a MUCH more effective way of harnessing solar energy for later use in the production of things.

- small vehicles aren't taken far (otherwise it's exhausting), so easily achievable 50-100 mile ranges are just fine

- small vehicles will have small, quickly, easily, cheaply rechargeable batteries, likely easily recharged from even plain old wall sockets

- LFP batteries will probably get good/cheap/dense enough to handle almost all 50-100 mile small vehicle ranges, its doubtful a hydrogen engine will get cheap enough soon enough

- and again, LFP and EV/battery tech is in the mainline of economies of scale, buildout, production, and cost cutting, and will be for a decade more. This stuff will need to compete at a price point 50% lower or less than today's.

- and it still has the sourcing problems. green hydrogen still smacks of the "clean coal" whitewash with a different label

The military has worked on a similar concept with a metal powder + water to produce hydrogen on the fly. https://en.wikipedia.org/wiki/Aluminium-based_nanogalvanic_a...

1) What happens to the waste? 2) How much energy is required to make the paste?

Why don't we "just" synthesize hydrocarbons similar to what are present in gasoline/diesel/etc? We already have all the infrastructure for using, handling and distributing it.

Because the well-to-wheel efficiency of internal combustion engines isn't that good to begin with. Add lossy synthesation and it gets even worse.

If we had unlimited, clean power (hello fusion!) it might be viable.

Really exciting news! I am a big believer in both small electric vehicles as the future of urban transportation and hydrogen as a better energy storage mechanism than lithium batteries. :)

I've wondered if aluminum powder could be used in this way. It's the most common metal in the world, cheap and available.

So, creating the Powerpaste is the hard thing?

Is the waste product Magnesium Oxide?

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