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Comment by _ph_ | Hacker News Reader

Unfortunately, splitting water into hydrogen and oxygen are only a part of the process. A lot of energy is wasted when the hydrogen has to be compressed for transport, storage and in the car. That makes hydrogen less attractive than batteries, even if we solve the inefficiencies of the hydrogen production.

However, it would be great news for many other fields. One way to make hydrogen more storable is to produce methane. And of course use hydrogen directly for industrial applications, like steel production.

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For transportation, hydrogen can be absorbed by a carrier oil. That way it is basically inert, doesn't even count as dangerous goods for transportation purposes. No compression needed. In cars it is different, so.

What’s the density of hydrogen using this method versus compression?

I'd have to look up the numbers. Cost wise, a pure hydrogen pipeline is cheaper for sure. At scale at least. Until that scale is reached, using carrier oil is much cheaper, but still competitive enough to get it going.

EDIT: The oil is called marlotherm something, if memory serves well.

It would be specially interesting for aviation, since the energy density of batteries is still too low for commercial aircraft. Airbus is pushing for zero emissions H2-powered planes: https://www.airbus.com/innovation/zero-emission/hydrogen/zer...

What makes hydrogen interesting in aviation is that it is possible to convert existing engine designs to burn hydrogen apparently. There have been a few tests with this recently.

Mid term, hydrogen is the obvious way to clean up the aviation industry. Basically as soon as hydrogen prices drop below kerosene prices, companies will start doing this by themselves because it makes economical sense. Right now it's more of an investment for the long term. Airbus is clearly betting that this is going to happen in the next two decades or so. If you look at clean energy cost dropping over time, they might be right about that.

Battery powered planes also make sense; just not for the bigger planes any time soon. But with another decade of battery improvements, GA planes & battery is going to be a no brainer-solution for a lot of use cases. Basically, this will be driven by cost. At some point battery powered is going to be cheap and good enough that the added advantage of low energy cost and vastly simpler/cheaper maintenance is going to be a killer argument. E.g. flight schools are already switching because it makes economical sense.

If you look at the R&D pipelines of companies in this space, ten years could solve a lot of issues. Think double/triple the range of current electrical planes at half the cost. Small planes are expensive to operate currently and fuel & maintenance are big factors here.

Completely correct, H2 either in fuel cells or burnt in turbines and battery-powered hybridization are two of the pillars of the EU's Clean Aviation R&D programme: https://clean-aviation.eu/files/Clean%20Aviation%20-%20Share...

It is going to be very costly (energy and capital investment) to convert steel making to use hydrogen. A blast furnace is a well balanced chemical reaction where the coke serves two purposes; a source of carbon monoxide for turning ore in iron (Fe2O3(s) + 3 CO(g) => 2 Fe(s) + 3 CO2(g), very exothermic, good for turning the iron / steel into a liquid alloy), and a source of carbon for turning the iron into steel. All in one vessel and in one process no less. I guess you could do the first step using peroxide to strip the oxygen from the iron, but the second step in the same vessel at the same time?

Fe2o3 + 3H2O2 => 2 Fe + 3 H2O, somewhat exothermic (if my rusty memory of enthalpy calculations are correct), not sure of the activation energy or need for catalysts).

[EDIT] also forgot the peroxide reaction would probably require external heat to over come the latent energy required to turn the H2O into super heated steam so that you could melt the iron / steel. This would probably boil off a large chunk of the peroxide as well, so it might need to be done in a contained pressure vessel, which would probably affect the speed of the iron ore reduction.

There is a steel mill that uses hydrogen, but it appears to be a recycling kind, rather than one that makes iron from ore with a blast furnace.

https://www.rechargenews.com/transition/-world-first-as-hydr...

Yes, I suspect this is much easier as you don't need to alloy as the steel is already alloyed with carbon.

I am not a steel expert, but the steel industry is constantly talking about converting to hydrogen. Your sum formula has a bit lot of oxygen, shouldn't it be Fe2O3+3H2 => 2 Fe + 2 H2O? In any case, they could use additional hydrogen for heating and burning it with ambient air.

I suggested using peroxide not hydrogen, as the peroxide reaction is more exothermic. Either way I suspect that you'd need to burn a lot of extra hydrogen to overcome the latent heat of water and create sufficient heat to melt the ore / alloy.

A quick back of the envelope calculation would be at least 1 million litres of H2 per ton of steel. So maybe 2~3 million litres of H2 per manufactured car just for the steel alone?

[EDIT] Peroxide also has the added benefit of being a liquid at room temperature.

Yes, peroxide being liquid certainly is nice, being a light gas is certainly one major obstacle in using H2. However I am surprised that the peroxide reaction would be more exothermic, as you would have to break the hydrogen from the peroxide first. 1 million litres of H2 are just 90kg though, that isn't that much for a ton of steel.

It is only a bit more exothermic, about 20% more (again from my rusty enthalpy calculations). The downside of course is making the peroxide in the first place.

Also, peroxide is relatively safe (compared to gaseous hydrogen) to handle up to ~150C.

I am reminded of the classic article "things I Won't Work With" by chemist Derek Lowe on the subject of Peroxides

https://blogs.sciencemag.org/pipeline/archives/2014/10/10/th....

they don't sound safe

Look here: https://www.hybritdevelopment.com/

Particularly the "Downloads" section, they have quite a bit of info reasonably easy to digest for interested lay people.

It may be expensive, but it's pretty much the only game in town. The only possible alternative is direct electrolysis, but that's even less developed. The hydrogen path is from what I understand technically not that much different from direct reduced iron with natural gas, which is something that already is in use for a significant chunk of steel production.

Thanks, it's a good source. Also on the financial front of how they organised finance and created a route to market.

The biggest steel mill in my state is switching to locally sourced green hydrogen. Written out, that sounds pretty funny. But it's produced with local solar energy farms, so it's pretty accurate.

This is one area where carbon taxes are the obvious solution. Cost and availability is the biggest driving factor for industry. Furnace coal is available and cheap, but if you tax it heavily for it's emissions enough it won't be. Will steel become extinct? Of course not, the mills will switch to the next alternative, which is hydrogen. It will be ripe with opportunity, with solar farms and hydrogen plants popping up around steel mills.

Already we are seeing coal plants written off as unprofitable and future mining projects are becoming less attractive to investors in an unpredictable future. Even without a carbon tax, we could see the cost of coal go up enough to make a local hydrogen industry make more sense. But we can speed the whole process up with smart carbon taxes.

The "Just have a think" youtube channel did a nice episode on this topic last week: https://www.youtube.com/watch?v=ywHJt88H5YQ

Apparently there are several viable ways to make clean energy work in this space. And there are some companies starting to do some of this already. Carbon prices is short term going to be needed to cover the price difference.

But the cool thing is that it boils down to cost per MWH of energy per tonne of steel. As that goes down, it becomes more viable and eventually cheaper.

Fe2o3 + 3H2O2 => 2 Fe + 3 H2O

This is not balanced correctly. There are 9 oxygen atoms on the left hand and only 3 oxygen atoms on the right hand.

Hydrogen peroxide can act as a reducing agent relative to some things, like permanganate anions, but it's an oxidizing agent relative to metallic iron. Hydrogen peroxide cannot substitute for coal or hydrogen in steel production.

Yup, you're right, rusty chemistry on my part.

When there is wind or sun, it's not entirely impossible to produce hydrogen on site - within limits of course. Then the question is what kind of energy storage is more cost efficient on the long run.

If there is sun why not skip the middle man and use an array of mirrors for direct heating?

Oh come on. Anyway, the sun doesn't shine at night. In the winter, the situation is difficult too. You need storage but you don't necessarily have to move the storage across countries.

The idea is to use water as the fuel and convert to hydrogen just in time for combustion.

How would that work? That sounds like a perpetual motion machine.

Like how a gun works, essentially a battery for the initial motion, using the subsequent motion storing some for the next initial motion.

Guns work by having chemical explosives in them. Which is also how gasoline powered cars work.

They definitely do not work by using a depleted battery to charge a second battery to create energy out of nothing.

gasoline cars also use a battery to initiate the engine.

Yes. However they don't use it to both power the car and charge the battery. Kickstarting the engine with a battery is very different from only having a battery and also using that battery to charge itself and the car at the same time.

The original poster was proposing a closed system where you would turn water into hydrogen (a very energy intensive process) and then turn it back into water (an energy releasing process) inside the car to provide all the energy. This is not how physics works. You cannot use your energy source to create more of your energy source without an external energy source. It just doesn't work that way.

No, it's not :)

Where would you get the energy to split the water? Why not just use that energy directly :).

The idea is to use the water as an energy carrier. You split the water into H2, than use that to power a car producing water as the only output.

If cars produce water as exhaust, will there be constant rain showers on congested roads?

They already produce plenty of water in the exhaust.

Right, I did a simple calculation, for the same distance driven, both gasonine and fuel cell cars produce pretty much the same amount of water, about 100ml/km. Only difference is, with gasoline that water is mostly vapour, so it doesn't get on the road so much, fuel cell cars have small tanks not to wet the road constantly.

Watch a YouTube of a hydrogen car review. They produce maybe a cup of water for a consider amount of driving. It’d evaporate relatively quickly.

>Where would you get the energy to split the water?

From a battery.

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