I was thinking about tanks wrapped with graphene tape, but looking into it, it's more complex.
Tiny little tanks:
Graphene-wrapped Nanocrystals Power New Fuel Cell Design
Hydrogen fuel out of thin air?
Graphene membrane allows mobile Fuel Cells to harvest Hydrogen straight from Air
It stops hydrogen and helium but water evaporates right through [graphene oxide]?
Graphene: Supermaterial goes superpermeable