[mppm]

> Storage tanks for compressed hydrogen enjoy the square-cube law.

Not really. Wall thickness is roughly proportional to diameter, and surface area to the square, so you don't gain anything in terms of storage mass ratio by building bigger tanks.

> But the round-trip efficiency of the tank is virtually 100%

This is oversimplifying quite a bit. Compressing hydrogen, the lightest gas, is very energy intensive per unit of mass, and this energy is not fully recoverable upon decompression (due to general pump efficiency and thermal losses in the intercooler).

[MobiusHorizons]

Also hydrogen loves to leak through tank walls, and can make metals brittle (this was covered in the article)