Imagine we have this electrolysis plant, splitting up water to produce the hydrogen we need for an area. That's fine.
But it needs fed electricity to keep the process going. Lots of it. It needs more electrical power to split the water than combining it again produces.
So it starts off being energy-negative, and it takes serious electricity to make it happen. Our grid isn't necessarily ready for that.
And then we need to transport the hydrogen. Probably with things like trucks and trains at first (but maybe pipelines eventually). This makes it even more energy-negative, and adds having great volumes of this potentially-explosive gas in our immediate vicinity some of the time whether we're using it individually or not.
Or: We can just plug in our battery-cars at home, and skip all that fuel transportation business altogether.
It's still energy-negative, and the grid might not be ready for everyone to do that either.
But at least we don't need to to implement an entirely new kind of scale for hydrogen production and distribution before it can be used.
So that's kind of the way we've been going: We plug out cars into the existing grid and charge them using the same electricity that could instead have been used to produce hydrogen.
(It'd be nice if battery recycling were more common, but it turns out that they have far longer useful lives than anyone reasonably anticipated and it just isn't a huge problem...yet. And that's not a huge concern, really: We already have a profitable and profoundly vast automotive recycling industry. We'll be sourcing lithium from automotive salvage yards as soon as it is profitable to do so.)
Also, compressing and cooling a gas takes another huge hit at the efficiency. Electrolysis comes out at atmospheric pressures.
Oh and the platinum electrodes you need…
I’m also just now visualising a hydrogen pipeline fire… terrible terrible idea.
Some advantages are that a fuel cell that accepts hydrogen and air at one end and emits electricity and water at the other can be lighter-weight than a big battery, and it can [potentially] be refueled quickly for long trips.
Some disadvantages: We need a compressed hydrogen tank -- which isn't as scary to me as it may be for some people, but that's still a new kind of risk we need to carry with us wherever we drive. And we still need a big(ish) battery and the controls for it in order for regen braking to do its thing (which hybrids have shown to be very useful).
And, again, the grid: If it were cheaper/better/efficient to move energy from electrical generating stations to the point of use using buckets [or trucks or trains] of hydrogen, we'd already be doing that. But it isn't. So we just plug stuff in, instead, and use the grid we already have.
A quick Google suggests that a regular 120v US outlet might charge EVs at a rate somewhere in the range of 3 to 5 miles per hour. So a dozen or so hours sitting, plugged in at home every day, is enough to cover most folks' every-day driving. There's far faster methods, but that's something that lots of regular people with a normal commute and normal working hours can already accomplish very easily if they have private parking with an outlet nearby.
For most folks, with most driving, that's all they ever have to do. It shifts concerns about refueling speed from "Yeah, but hydrogen is fast! I waste hardly any time at all while it refills!" to "What refueling stops? I just unplug my car in the morning and go. I haven't needed to stop at gas station in years."
The main advantages of hydrogen are real, but they just aren't very useful compared to other things that we also have.
And this gets significantly better once you start using 240v sockets - like the US is already using for dryers. Got a dryer in your garage? Guess what, you are only a weekend project away from having an overnight EV charger in your garage!
My main point is that many of us have a perfectly-usable method within reach that provides enough juice to keep the car going day after day for the driving we normally do, which can be used right now without knowing what a screwdriver even looks like.
Just buy the car and drive it to work tomorrow (and the next day, and the day after that), and leave it plugged in while it sits there at home. This is exactly what the folks I know who drive EVs and who do fast chargers already do; it's a habit for them. They get home, and if they don't plan on leaving again soon then they plug their car in.
Except: There's not even necessarily any weekend project required -- for most drivers, faster charging at home is completely optional. Needs vary, but for most people it maths out fine to just use the regular ass-plug[1] that's already right there on the wall.
Even for longer trips: Visiting family, out of town, overnight? No problem. Plug your car in after you get settled in. No big deal. It doesn't matter if they're an EV family or not; while the car is just sitting there, it may as well also be taking a charge. (As to the cost: Buy them a beer or something and fuhgettaboutit.)
[1]: https://xkcd.com/37/
It is actually less dangerous than other fuels, for the simple reason that it is extremely light and buoyant. A gasoline fire is bad, because the gasoline stays where it is until it fully burns. A hydrogen fire is less bad, because it will tend to move upwards.
If you assume a realistic fuel capacity for a hydrogen vehicle, the hydrogen tank will be both much larger than a gas tank and the hydrogen will be under extreme pressure. A tank like that in your car would be extremely dangerous even if it were filled only with inert gas.
1: https://www.thenewatlantis.com/publications/the-hydrogen-hoa...
Interestingly, liquid hydrogen is nowhere near the most energy-dense way to store and transport it. I don't recall the exact numbers but absorption in a rare-earth metal matrix is said to be much better on a volumetric basis. [1] Still not exactly cheap or convenient, but it mitigates at least some of the drawbacks with liquid H2.
1: https://www.fuelcellstore.com/blog-section/what-hydrogen-sto...
(In some future decade/century, people might conclude that car dependency on fossil fuels, after electric from renewable became viable, was a mistake.)
(Separate to whether the idea originally made sense back in the 2000s.)
Japan could have simply started their own refining business if they were really worried about REEs in 2010. Yes, it would take them until 2015 or so to ramp up, but that was still 11 years ago.
Why wait though ;)
With common metals hydrogen fits in between the matrix naturally to an extent.
Not like for efficient storage though, just the embrittlement, which gives researchers even more challenging things to be careful about.
Correction, a very low density, lightweight fuel.
Burns clean though with no carbon in the exhaust.
But the upstream carbon emissions have not come close to zero when you look at total hydrogen use in the real world so far.
Hydrogen wastes a large amount of energy.
See: https://en.wikipedia.org/wiki/Sulfur%E2%80%93iodine_cycle
and: https://www.jaea.go.jp/04/o-arai/nhc/en/research/hydrogen_he...
It's hard to work with because of this, and what's the point? For most uses, electricity supply is already everywhere.
Wait until you hear about H+
(Atoms must have electrons - the definition in physics and chemistry is a structural one.)
The basic point is that a material that is highly flammable, needs to be compressed to high pressure in order to be useful, but also will seep through and damage steel containers because of the fundamental fact that the atoms and charged ions are just too small, is never going to be easy to work with. Compared to electrical battery tech now being widely and cheaply rolled out.
This goes some way to answering the "Why is it such a terrible idea?" question. Or at least it's an idea whose time has passed, due to the abovementioned battery tech maturing.