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.
https://www.linkedin.com/pulse/clean-hydrogen-ladder-v40-mic...
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 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.
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.
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?
In practice, hydrogen cars are quite safe. They're just not worth the cost in infrastructure and lack of efficiency compared to BEVs.
Two words: Attached Garage
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.
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.
[1] https://www.history.com/news/the-hindenburg-disaster-9-surpr...
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.
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.
