The big problem with using hydrogen for fuel is that it’s a gas. The combustibility of the gas is of little matter when it comes to using it as a transportation fuel. The problem is that in order to have enough of it to get anywhere, you have to liquefy it. There are two ways to do this, temperature and pressure.
The space shuttle uses liquid hydrogen as a fuel source, but stores it cryogenically, which is why the fuel tank has to be insulated with foam that likes to occassionaly fly off and damage the heat shielding. Cryogenic storage is expensive and impractical for use in earth bound transportation. It’s really impractical and too expensive for rockets too, but the alternatives kind of suck.
The other option is to pressurize the hydrogen to such a degree that it becomes a liquid at normal atmospheric temperatures. The first trade off in this kind of scheme is that it takes about 30% of the energy stored in the hydrogen to get it to a liquid state. The other major disadvantage to storing hydrogen in liquid state is that it has to be stored at about 10,000 psi, which is essentially bomb. And not just any bomb, a bomb that will spew cryogenic liquid everywhere.Â There’s also the issue with the tank material needing to stand up to wide temperature fluctuations as you start to draw off hydrogen, thus cooling the liquid down to a cryogenic state.
The other solution is to store it as a gas a very high pressures. This still has the problem of creating a bomb. It’s not the combustibility of the gas that’s a problem, it’s the energy stored up as pressure.