At what, 20 times the volume?
Plus, for the scientifically illiterate, because you can’t mine/drill for hydrogen on earth, it is effectively an energy storage mechanism, not a source of energy.
Meaning just like your electric car, your hydrogen powered car/jet/whatever is ultimately powered by fossil fuel anyway.
Only if you haven't come up with a better source of electricity than fossil fuel*. Note that you can use hydrogen as a grid storage mechanism. That helps with power sources that run when they want to (= wind, solar) and power sources that can't be effectively throttled-down at night (= nuclear, coal to some extent).
*Fossil fuel can generate hydrogen directly, without going through electricity. The direct path is much more efficient, of course.
I think gasoline has about 3000 times the energy of hydrogen at STP.
I maintain that the key to this tech is the efficient generation of hydrogen via an onboard on-demand closed-loop electrolysis system. In addition, plasma plugs similar to that which were developed by Meyers would be required among other “enhancements”.