the biggest problem is freeing enough hydrogen to power anything... burning hydrogen doesn't release as much energy as it took to make the hydrogen...

hydrogen fuel cells work... make electricity to do work efficiently.

the hydrogen embrittlement of steel and aluminum is another problem too for burning hydrogen...

methane is a much better choice, and still a difficult fuel... 3000 psi vs 300, larger tanks and the fuel still evaporates out of the tanks...

LPG is the easiest of the liquid cryogenic fuels to store and handle and run an engine on...

to liberate enough hydrogen to mix with 100 cf/m may prove to be a bit harder... you need something like 1cf/m of hydrogen at atmospheric pressure... quite a bit to make with electrolysis...