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.
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.
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...
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.)
It's hard to work with because of this, and what's the point? For most uses, electricity supply is already everywhere.