Hydrogen sucks to work with, from everything I've heard. In addition to the combustion risk when oxygen is introduced, there's the fact that hydrogen molecules are tiny and like to slip through otherwise solid materials, which is annoying if you're trying to fuel a rocket, but it's eventually catastrophic for containment vessels, due to hydrogen embrittlement[1]. As tempting as it is for its benefits, I don't see it being worth the long-term risks and engineering trades.
I've worked with hydrogen (H2) quite a bit recently. Embrittlement and leakage are easy to work around, but here are the pain points I've seen:
1. H2 is still expensive. Most fuel cells require very pure H2 (five nines; 99.999%), or else it can damage the internal membrane. This pure H2 is not very affordable outside of a limited number of fuelling stations.
2. The rules around H2 use and transportation are still fuzzy. Despite being around for so long, regulations are still lacking or unclear.
3. H2 is light weight but takes up a lot of volume, limiting the usefulness of small-scale applications. Compressing it to liquid takes a lot of energy.
4. Fire/explosion risks, as you mentioned.
5. Fuel cells are expensive. If you look at financial statements for most fuel cell companies, they are selling them at a loss, meaning most fuel cells sold today are subsidized by government grants and investors.
6. The oil/gas industry is still pushing "grey" and "blue" hydrogen, which uses natural gas and emits carbon to produce H2.
I think H2 will play an important role, especially in decarbonizing steel making and large transportation applications, but people need to be aware of the limitations and longer timelines required for widespread adoption of green H2.
I love the hydrogen ladder to visualize this concept. To decarbonize fertilizer hydrogen is unavoidable, for personal transports it has been uncompetitive the past decade.
> 3. H2 is light weight but takes up a lot of volume, limiting the usefulness of small-scale applications. Compressing it to liquid takes a lot of energy.
My understanding is that H2 is seeming to standardize upon 300-bar (aka: 4500ish PSI).
There's liquid and a few other more difficult storage (700-bar / 10,000 PSI for example). But 300-bar is where a lot H2 stuff is standardizing today.
Its not quite as dense as in liquid form, but it starts to be usable at 300-bar. Of course, the thicker and heavier steel needed to hold H2 at this pressure makes it unsuitable for say... drones. But its more than usable for H2 Forklifts and other smaller vehicles.
> Kilmartin said one of the questions he asked when he first got into the business was “who came up with this idea? He had to be a madman.”
Kilmartin should spend more time around rocket scientists. After hearing a few tales of some of the stuff they've come up with in the name of performance - like a Hydrogen/Lithium/Fluorine(!) tripropellant engine (but you get an Isp of 542s!!!) - using Hydrogen for cooling will sound positively tame, and easily controlled.
Rocket science as a field moved out of exotic energetic fuels by the end of the 90's, because the juice wasn't worth the squeeze, and there is currently an ongoing industry-wide exodus from hydrogen to methane for the same reason.
Getting the peak of performance sounds cool when you ignore costs, but in the real world with limited budgets, building a rocket twice as large is easily worth it if it means you never have to touch liquid hydrogen.
> there is currently an ongoing industry-wide exodus from hydrogen to methane for the same reason.
Exodus seems a bit of an overstatement. Other than spacex who else has or is planning to develop a methane engine? And other than SSME and Vulcain which other widely used engines used H2?
What Karellen said, but also ArianeSpace (Prometheus) and Landspace (TQ-12).
It is very hard for a hydrogen-fueled rocket to be cost-competitive against a methane-fueled one. Not strictly because of the cost of the fuel, but because of the cost of everything else that LH requires that LCH4 doesn't.
Not really - hydrogen shoots straight up into the atmosphere, whereas petrol both pools in the area and also turns to gas and mixes with air quite easily (which is why it's used as a fuel in the first place)
In practice, hydrogen cars are quite safe. They're just not worth the cost in infrastructure and lack of efficiency compared to BEVs.
It also depends on storage method. Cryogenic and compressed hydrogen have extreme risks completely unrelated to the flammability of the gas itself, while various metal hydride options are mostly a danger if you drop the tank on your foot.
> They're just not worth the cost in infrastructure and lack of efficiency compared to BEVs.
Don't BEVs weigh more than hydrogen cars, given the same model and range? That would give at least some incentive to use hydrogen over BEV, as it decreases road wear, which reduces the costs associated with the operation of that car.
Additionally, hydrogen cars could be considered safer once they've gotten into an accident, as risk of battery thermal runaway wouldn't usually be an issue for extended periods of time in hydrogen cars, whereas several car carrier ships have been lost due (in part or in full) to battery fires.
Even if car registration was taxed completely commensurate with their road wear (i.e. weight) the difference wouldn't be enough to move people over from BEV given the lack of refilling options.
Gas still has the infrastructure, but batteries are closer to having what they need than hydrogen for critical adoption.
Unless you're in the upper Midwest and your car is one of those stuck at a charger unable to fast charge because it's too cold and you didn't have an hours worth of time and energy to preheat it.
> Unless you're in the upper Midwest and your car is one of those stuck at a charger unable to fast charge because it's too cold and you didn't have an hours worth of time and energy to preheat it.
You also have the problem where it is "too hot". Higher battery wear and all. Part of me feels the BEV revolution only considered half the northern hemisphere.
Tons of EVs on the roads in Texas. I realize there can be hotter places (Death Valley) or more humid but certainly if you can drive an BEV in the height of Texas summer that should fit more of the worlds use cases.
I think cold is a harder problem to solve, I think your delta T of environment temps and operating temps are much greater in cold weather.
Exactly. People freaking out over EV infrastructure haven't done the math - nearly all first world home electric hookups are fine for charging a couple of EVs
Right since we haven’t already used an equal or even more so flammable substance for the past century
As far as I’m aware gasoline ignites at much lower mixtures of oxygen than hydrogen. The Hindenburg can’t hurt you and if it was filled with gasoline vapors instead of hydrogen, well it would never get of the ground, but it would have been more dangerous.
Nope. Hydrogen is not just flammable, the article tells you it is EXPLOSIVE at concentration of 4 percent to 74 percent in air. If the Hindenburg was a hydrogen-air mixture, it would have leveled a large portion of the area rather than just burning where it fell.
I've worked in areas where they were developing hydrogen fuel cell vehicles at major auto makers. The facilities are equipped with collectors, detectors, and alarms, and everyone knows to GTFO if the alarm goes off. Hydrogen leaks indoors are extremely dangerous.
One time I filled a Mylar balloon with H2 by electrolysis. It floated very nicely but I was too cowardly to keep it in the house. It made a nice fireball when lit outside but no particularly notable explosion.
Encouraged by this I filled one of those grocery store vegetable bags with H2 + O2 from the same electrolysis setup (combine both outputs this time). Stoichiometric mixture! The boom was so loud I thought it was going to break my windows from about 20 feet away.
The Hindenburg is a largely misunderstood incident [1]. It was one of the safest airplane crashes of the century. As the balloon burned, flames and gasses vented upwards, keeping the cabin and passengers under the balloon safe. Moreover, the balloon descended slowly as the hydrogen was replaced by air. So slowly that most people got off once it was close to the ground. Out of 97 people only 35 died.
Hydrogen is significantly more dangerous than gasoline; and gasoline is crazy dangerous as it is.
Lower spark energy
Broader range of combustibility
Faster detonation speed (? [1])
It's only positive is it dissipated quickly, but that's not that great because it goes boom boom at 5% H2 -air. Everyone I know who has worked on combustion problems (I haven't myself, but colleagues have) give H2 a lot of respect.
[1] this one is an educated guess on my part based on the thermo.
>Lower spark energy. Broader range of combustibility ...
But not at the same time. That is important because H2 has such a wide ignition range. At the lower end of concentration it isn't much easier to ignite than other things. A readable discussion:
Gasoline is an easily-contained liquid. Gasoline-vapor/air mixtures explode under relatively limited circumstances. Vs. hydrogen is a difficult-to-contain gas, the concentration range for hydrogen/air to be explosive is extremely wide, and triggering the explosion is extremely easy.
While I do not argue the explosive nature of it, safety can be improved by embracing how fast it disperses. Think Toyota went that path with interleaved fibers in their containers' outer enclosures, to augment that effect, so it isn't sufficient for an explosion to occur.
But a hydrogen / air mixture is explosive from 4% hydrogen to 74% hydrogen, Americans love their attached garages, and most attached garages feature a perfectly-placed electric spark detonator...er, I mean electric garage door opener...which is triggered daily.
I was not clear - I agree with you. I was saying that gasoline might be explosive, but it is not likely to happen. it is remarkably tolerant of heat/spark at STP conditions.
If you want to get really nuts: consider that high temperature superconductors are a good match for hydrogen cryogen coolant. Hight temperature superconductors work with liquid nitrogen, but work best with liquid helium and there just isn't that much helium in the world compared to how much superconducting magnets we could use.
Another reason hydrogen is good for cooling is its low viscosity.
The low viscosity is the reason the energy needed to transport hydrogen by pipeline is only slightly higher than natural gas, even though the combustion energy per molecule is considerably lower.
https://en.wikipedia.org/wiki/Hydrogen_embrittlement