Water vapor is a much more potent warming agent then CO2.
And it takes more energy to generate H2 then you get back when you “ burn “ it.
That H consumes more energy than released is immaterial. The goal is PORTABLE ENERGY. Energy that a vehicle can carry with it away from any real source.
Just like any battery — you lose more than you get, but what you get lets you drive around.
As to the danger of H, not really. H gas is formed of such small molecules that it almost instantaneously disperses given any puncture to its tank. Gas, on the other hand hangs around and burns the crap outta everything within reach.
Yah, the Hindenberg was filled with H. But, much of the flames were from burning structural material. Regardless, it was not on the ground — which doomed many on board.
IMHOpinion, H’s advantage is you can make it anywhere. If you can get electricity to a regular gas station you can have a separator there, too. This means no gas lines, no trucks , etc. Lots of companies in the energy sector hate this. Freedom, yknow.