It's the smallest molecule there is. It's really difficult to contain. It will leak out of steel containers while embrittling the metal. However it's not necessary to use pure hydrogen as vehicle fuel. Alcohol or other hydrocarbons can be used directly in a fuel cell to produce electric power, or be burned in an more traditional combustion engine.

Helium is the smallest molecule. H2 is quite a bit bigger.

Helium is the smallest atom iirc helium doesn't have a molecule.

the helium atom IS its molecule..

Hydrogen leaks out of steel containers because it's "small"? Doesn't the size of even the largest atom (or, for that matter, molecule) pale in comparison to even the smallest leaks you will typically find in a steel container?

It's not normal leaks. It's about hydrogen and helium diffusing through the container.

The Hindenburg had some other problems, too. The paint on the outside was extremely flammable.

(And still, casualties came mostly from people jumping off the ship. The people that stayed on mostly survived.)

The thing that made the Hindenburg transformative is that it was caught on film. After everyone had seen the disaster for themselves, they were never going to trust the technology again.