Hydrogen does have an extremely high energy density by weight. Unfortunately, it weighs almost nothing, which means you need a lot of it.

Might look at the following video, especially at the 1:40 mark where it shows the fuel cell, the tanks, the EV-style battery, the electric motor, and all of the other complexities needed to make a H2 vehicle "practical".

https://www.youtube.com/watch?v=rtZQLUtckS4&t=132s

Might also want to look at Michael Barnard's take on H2.

https://medium.com/the-future-is-electric/hydrogen-for-energy-pure-plays-skid-further-into-irrelevancy-e6d4aa62cf6e

Physics is physics. You're never going to get electricity to H2 back to electricity to be more efficient than simply using the original electricity.