6 ms·

Aside from the (obvious) energy density downside of hydrogen as a fuel, there is another substantial problem. Hydrogen is challenging/expensive to store/contai

Aside from the (obvious) energy density downside of hydrogen as a fuel, there is another substantial problem. Hydrogen is challenging/expensive to store/contain. Kind of the direct result of it being the smallest atom we have. Even more important: when it reacts uncontrolled, in particular with oxygen, it does so at a truly frightening speed. Once it goes, good luck doing anything about it. The fact that this is almost never mentioned in every yet-another-hydrogen-is-going-to-be-our-future-next-year piece, always makes me wonder if that's the result of not-so-honest entrepreneurs trying to lure investors, or that none of these jokers ever talked to any experienced chemist. This is no attempt to spread FUD regarding hydrogen. It sincerely worries (if not frightens) me, how so many initiatives appear to completely ignore that any volume of hydrogen that is sufficient to power something that can transport humans or cargo, is pretty much inherently a catastrophic disaster in the making. That is, if such a system would ever fail in a way that makes the stored hydrogen react uncontrolled. Every widely utilized technology is bound to fails, even if only in edge cases, and of course: extra safety margins/features can be added to limit the effects of failures. But with hydrogen that might be a hell of a lot more expensive and/or difficult than most would realize. So, the way I see this is that we either end up very cost ineffective solutions, or ones that will be far more dangerous than many would ever realize. That is, until something goes terribly wrong, and everyone realizes they have been ignorant and maybe even intentionally fooled by people trying to make money. Reminds me a bit of self-driving cars.

jeffreyrogers 6y ago
If your fuel tank catches on fire you have similar problems, so I don't think these problems with hydrogen are insurmountable.
- nitrogen 6y ago
  Gasoline is pretty well-behaved until it's vaporized.
  - jacquesm 6y ago
    That goes for lots of things including powdered sugar and flour. But that vaporization step usually happens in a relatively controlled environment which makes it manageable.
    - masklinn 6y ago
      Isn't that their point? That gasoline is a pretty well-behaved and easy to work with liquid while hydrogen isn't?
- paledot 6y ago
  Kerosene burns, hydrogen explodes. And kerosene doesn't actively damage the tank it's stored in, like hydrogen does.[1] Also, while its energy density per kilogram compares favourably to kerosene, its energy density per litre does not. Hydrogen is a great rocket fuel because its specific impulse is second to none, so why isn't it universally used? Because even by rocket fuel standards it's a bugger to work with. There are lots of things that react poorly to being set on fire. That doesn't make them all equally dangerous. [1] https://en.wikipedia.org/wiki/Hydrogen_embrittlement https://en.wikipedia.org/wiki/Hydrogen_embrittlement
  - jeffreyrogers 6y ago
    Hydrogen embrittlement depends on the type of tank. It does not occur with every material. Look, I'm not saying hydrogen is great and has no problems. I'm saying the problems are not in theory insurmountable. I have elsewhere made the same point as you with regards to mass vs volume. I'm aware of the drawbacks of hydrogen and am actually pessimistic on its use in aviation, but I think it is worth trying out.
    - jacquesm 6y ago
      Hydrogen is not only in contact with the tank but with other materials en route to the fuel cell as well. And the problems don't need to be insurmountable in theory, they need to actually be solvable and that is a different thing entirely. I'm fine with people trying it out but I'm very skeptical about this ever making it to production. I think this is more of a PR piece than anything substantial.
      - masklinn 6y ago
        > Hydrogen is not only in contact with the tank but with other materials en route to the fuel cell as well. Isn't it also in contact with everything around the tank on account on there being basically nothing which is completely impermeable to hydrogen?
      - jeffreyrogers 6y ago
        I don't think hydrogen powered planes will substantially replace normal planes for reasons having to do partially with safety and partially with performance, but I think the engineering problems are surmountable. There are existing prototypes that have flown using hydrogen fuel cells, and the Tu-155 which ran on liquid hydrogen (used as fuel for its jet engines though, not to power fuel cells). So it's not like this stuff doesn't work. I think you are overestimating the difficulty of dealing with embrittlement. Many materials don't suffer from embrittlement at all, and others (like aluminum) only suffer at high temperatures. Edit: I also wanted to add to the person who made the claim "kerosene burns, hydrogen explodes" that kerosone can explode too, and it obviously is possible to handle hydrogen in a way that explosion is unlikely or it wouldn't be used as rocket fuel (where it is literally combusted with oxygen... combusted, not exploded). I agree that hydrogen is more dangerous than kerosene, but it's not like kerosene is that safe either and the question is whether you can create good enough processes around the storage and handling of hydrogen to offset the risk.
- elmo2you 6y ago
  It's the huge difference in reaction speed that makes all the difference. Even in their gaseous/vaporized forms, conventional (fossil) fuels react comparatively slowly compared to hydrogen, like a sweet retriever puppy compared to a trained dog of war. It's exactly this difference that makes them relatively safe to use and even still relatively controllable once something goes wrong. With hydrogen, you simply won't get that change. It will be all over in a blink. A very hot and bright one, I might add. Feel free to believe whatever you want, you have every right. But I'm rather sure that your optimism regarding hydrogen is more rooted in ignorance than in knowledge.
  - jeffreyrogers 6y ago
    Yeah, I'm actually more familiar with hydrogen than you think. I'm aware of the problems with reaction speed. One advantage hydrogen has is that it escapes very rapidly from its container and goes pretty much straight up due to how light it is. I'm actually not as much of an optimist on hydrogen as you seem to think. I think it is unlikely to be used in aviation in any real sense, for a variety of reasons, some having to do with safety, others with performance. However, I think it is worth investigating, and I do not think the problems around it are insurmountable from an engineering perspective.
    - elmo2you 6y ago
      Fair enough. Thought then I'm sincerely even more surprised you would say that any fuel tank on fire is a (relatively) equal problem. As for hydrogen rapidly escaping and going straight up because of its low density, those properties I would only consider positive in scenarios where the hydrogen isn't reacting (being on fire, to be more precise). When on fire, quite the opposite. Buildup of heat on the ground might still be less of a problem than with heavier fuels (which indeed is a very real problem with those), but not much advantage of that once everything within a certain radius is reduced to the size of matchsticks by a powerful explosion. But if you claim to be (some sort of) an expert, I'll believe you. I certainly am not, that much I admit. I only based my opinion on what I've been told by chemists that I personally trust. They told me rather invariably that the engineering challenges for storing/operating hydrogen are such a bitch, that they are ultimately only a good for when you want something closely resembling a bomb, without actually being one (or just hoping it won't explode before it served its purpose). Like e.g. rocket engines.
jonsen 6y ago
It seems like you are not aware of existing production of hydrogen cars: https://en.m.wikipedia.org/wiki/Toyota_Mirai https://en.m.wikipedia.org/wiki/Toyota_Mirai
- elmo2you 6y ago
  That particular model? No, I was not aware of it. But that production hydrogen cars exist, yes I did. However, proof of their existence isn't proof of their safety. I have no doubt that they are (mostly) safe, even in almost every imaginable accident. However, it's the (unforeseen) edge cases that worry me. Not because of how often they might happen, but because of how bad the consequences could be when things go wrong. It's a real bummer when whole a housing block gets wiped of the map, because one eccentric/rich guy just had to do something "for the environment" (#sarcasm). From what I read, this car has storage capacity of 5 kg of pressurized hydrogen. I've seen similar storage tanks, and I have been amazed about how resistant they are to puncturing and tearing forces. Unlikely that any direct impact collusion would destroy one of these. But then there is always some corner case that it wasn't designed for. I certainly would not like to be even remotely around it, when 5 kg of pressurized hydrogen goes up in flames. As hopefully every engineer knows, catastrophic failure is almost always a cascade of smaller compounding failures. Disrupt that chain-reaction and a catastrophe is usually averted. However, with hydrogen the opportunity/window for that is often extremely short, with extreme consequences as a result. Not quite what you might call an optimal combination of factors. Technically we could drive cars on nuclear reactors.
  - jonsen 6y ago
    Substantially more than 5kg of hydrogen went up in flames with the Hindenburg, but I don’t think anything was wiped off the map there. Do you have any reference to the actual danger of stored hydrogen?
    - walrus01 6y ago
      It's the tank pressures that make stored hydrogen almost indistinguishable from a bomb. 350 to 700 bar is not uncommon. For comparison 7 bar is about the same as 100 psi for Americans.

jeffreyrogers 6y ago

If your fuel tank catches on fire you have similar problems, so I don't think these problems with hydrogen are insurmountable.

nitrogen 6y ago
Gasoline is pretty well-behaved until it's vaporized.
- jacquesm 6y ago
  That goes for lots of things including powdered sugar and flour. But that vaporization step usually happens in a relatively controlled environment which makes it manageable.
  - masklinn 6y ago
    Isn't that their point? That gasoline is a pretty well-behaved and easy to work with liquid while hydrogen isn't?
paledot 6y ago
Kerosene burns, hydrogen explodes. And kerosene doesn't actively damage the tank it's stored in, like hydrogen does.[1] Also, while its energy density per kilogram compares favourably to kerosene, its energy density per litre does not. Hydrogen is a great rocket fuel because its specific impulse is second to none, so why isn't it universally used? Because even by rocket fuel standards it's a bugger to work with. There are lots of things that react poorly to being set on fire. That doesn't make them all equally dangerous. [1] https://en.wikipedia.org/wiki/Hydrogen_embrittlement https://en.wikipedia.org/wiki/Hydrogen_embrittlement
- jeffreyrogers 6y ago
  Hydrogen embrittlement depends on the type of tank. It does not occur with every material. Look, I'm not saying hydrogen is great and has no problems. I'm saying the problems are not in theory insurmountable. I have elsewhere made the same point as you with regards to mass vs volume. I'm aware of the drawbacks of hydrogen and am actually pessimistic on its use in aviation, but I think it is worth trying out.
  - jacquesm 6y ago
    Hydrogen is not only in contact with the tank but with other materials en route to the fuel cell as well. And the problems don't need to be insurmountable in theory, they need to actually be solvable and that is a different thing entirely. I'm fine with people trying it out but I'm very skeptical about this ever making it to production. I think this is more of a PR piece than anything substantial.
    - masklinn 6y ago
      > Hydrogen is not only in contact with the tank but with other materials en route to the fuel cell as well. Isn't it also in contact with everything around the tank on account on there being basically nothing which is completely impermeable to hydrogen?
    - jeffreyrogers 6y ago
      I don't think hydrogen powered planes will substantially replace normal planes for reasons having to do partially with safety and partially with performance, but I think the engineering problems are surmountable. There are existing prototypes that have flown using hydrogen fuel cells, and the Tu-155 which ran on liquid hydrogen (used as fuel for its jet engines though, not to power fuel cells). So it's not like this stuff doesn't work. I think you are overestimating the difficulty of dealing with embrittlement. Many materials don't suffer from embrittlement at all, and others (like aluminum) only suffer at high temperatures. Edit: I also wanted to add to the person who made the claim "kerosene burns, hydrogen explodes" that kerosone can explode too, and it obviously is possible to handle hydrogen in a way that explosion is unlikely or it wouldn't be used as rocket fuel (where it is literally combusted with oxygen... combusted, not exploded). I agree that hydrogen is more dangerous than kerosene, but it's not like kerosene is that safe either and the question is whether you can create good enough processes around the storage and handling of hydrogen to offset the risk.
elmo2you 6y ago
It's the huge difference in reaction speed that makes all the difference. Even in their gaseous/vaporized forms, conventional (fossil) fuels react comparatively slowly compared to hydrogen, like a sweet retriever puppy compared to a trained dog of war. It's exactly this difference that makes them relatively safe to use and even still relatively controllable once something goes wrong. With hydrogen, you simply won't get that change. It will be all over in a blink. A very hot and bright one, I might add. Feel free to believe whatever you want, you have every right. But I'm rather sure that your optimism regarding hydrogen is more rooted in ignorance than in knowledge.
- jeffreyrogers 6y ago
  Yeah, I'm actually more familiar with hydrogen than you think. I'm aware of the problems with reaction speed. One advantage hydrogen has is that it escapes very rapidly from its container and goes pretty much straight up due to how light it is. I'm actually not as much of an optimist on hydrogen as you seem to think. I think it is unlikely to be used in aviation in any real sense, for a variety of reasons, some having to do with safety, others with performance. However, I think it is worth investigating, and I do not think the problems around it are insurmountable from an engineering perspective.
  - elmo2you 6y ago
    Fair enough. Thought then I'm sincerely even more surprised you would say that any fuel tank on fire is a (relatively) equal problem. As for hydrogen rapidly escaping and going straight up because of its low density, those properties I would only consider positive in scenarios where the hydrogen isn't reacting (being on fire, to be more precise). When on fire, quite the opposite. Buildup of heat on the ground might still be less of a problem than with heavier fuels (which indeed is a very real problem with those), but not much advantage of that once everything within a certain radius is reduced to the size of matchsticks by a powerful explosion. But if you claim to be (some sort of) an expert, I'll believe you. I certainly am not, that much I admit. I only based my opinion on what I've been told by chemists that I personally trust. They told me rather invariably that the engineering challenges for storing/operating hydrogen are such a bitch, that they are ultimately only a good for when you want something closely resembling a bomb, without actually being one (or just hoping it won't explode before it served its purpose). Like e.g. rocket engines.

jonsen 6y ago

It seems like you are not aware of existing production of hydrogen cars: https://en.m.wikipedia.org/wiki/Toyota_Mirai https://en.m.wikipedia.org/wiki/Toyota_Mirai

elmo2you 6y ago
That particular model? No, I was not aware of it. But that production hydrogen cars exist, yes I did. However, proof of their existence isn't proof of their safety. I have no doubt that they are (mostly) safe, even in almost every imaginable accident. However, it's the (unforeseen) edge cases that worry me. Not because of how often they might happen, but because of how bad the consequences could be when things go wrong. It's a real bummer when whole a housing block gets wiped of the map, because one eccentric/rich guy just had to do something "for the environment" (#sarcasm). From what I read, this car has storage capacity of 5 kg of pressurized hydrogen. I've seen similar storage tanks, and I have been amazed about how resistant they are to puncturing and tearing forces. Unlikely that any direct impact collusion would destroy one of these. But then there is always some corner case that it wasn't designed for. I certainly would not like to be even remotely around it, when 5 kg of pressurized hydrogen goes up in flames. As hopefully every engineer knows, catastrophic failure is almost always a cascade of smaller compounding failures. Disrupt that chain-reaction and a catastrophe is usually averted. However, with hydrogen the opportunity/window for that is often extremely short, with extreme consequences as a result. Not quite what you might call an optimal combination of factors. Technically we could drive cars on nuclear reactors.
- jonsen 6y ago
  Substantially more than 5kg of hydrogen went up in flames with the Hindenburg, but I don’t think anything was wiped off the map there. Do you have any reference to the actual danger of stored hydrogen?
  - walrus01 6y ago
    It's the tank pressures that make stored hydrogen almost indistinguishable from a bomb. 350 to 700 bar is not uncommon. For comparison 7 bar is about the same as 100 psi for Americans.