As for how long before we see them, who knows. California (of course) has a limited hydrogen distribution system and has had some fuel-cell cars available in very limited areas, I supposed a "let's-see-how-this-works" program. I know of several companies developing hydrogen ICE cars but I know of no commitments for availability.
I have seen hydrogen proposed as both a fuel for fuel cells, generating electricity for electric drive and as internal combustion engines not much different than what we use for gasoline.
Fuel-cell cars would still have batteries, but they don't need anywhere near the size battery pack that a non-fuel-cell EV needs, the fuel cell charges the battery and supplies power to the motor, and the battery can be tapped for higher energy into the motor than the fuel cell can deliver alone.
Hydrogen internal combustion uses an engine like we're all familiar with, and the exhaust even sounds close to what we're used to.
The problem with hydrogen is it's hard to get. It may be the most abundant element on Earth, but its atoms are always bonded with others into compounds, like water. Producing hydrogen is itself energy-negative; it takes more energy to get it than the hydrogen contains, so whatever powers your hydrogen production may not be as green as one would hope.
I saw someone above mention that it has to be stored cold, but that's not true; it simply has to be stored at
very high pressure. Rockets store it cryogenic fuel because they couldn't lift a tank strong enough to store it at something like 10,000 psi.
The advantage of hydrogen over pure electric is that refueling is on par with gasoline refueling, and nowhere near the time required for charging a battery. The disadvantage relative to both EV and petroleum fuel is cost and infrastructure, and of course proponents promise that both will get better with wide adoption. I'm no civil engineer, but personally, I think (purely a guess) that a hydrogen infrastructure would be much easier to build than rebuilding the electrical grid so every family can have two or three or four electric cars.
As for refueling, it looks to be on par with filling a gas tank. No need to plan your stops around meals or some other place to kill time.
I just saw
@Exorcet's mention of induction charging on the road. How does that work, exactly? If you can insert energy into an EV as it travels, why not just power it like that? (Simplistic question, I know, but I'd never seen that referred to before.)
