[R0b0t1]

There are iirc substances like graphite(?) sponge that will take in more H2 at a given pressure. It's still high, but it's better. The tanks can be made long and thin and stacked. Is the extra tank material too much in either cost or mass?

[jonititan]

I haven't looked at the various sponge or chemical binding concepts personally. To be used in an aircraft to be delivered say in 10 years time they would already need to have been approved by EASA or FAA or have a clear and straightforward approval pathway. Otherwise they represent a large schedule risk and new airliner types cost several billion to launch so they are pretty risk averse.

That's not to say those concepts won't work. Regarding long thin tanks wings don't actually have that much suitable internal volume for that. Lots of ribs, stringers, etc. That's why most hydrogen aircraft concepts use under wing pods or fuselage tanks to store the hydrogen even though it reduces safety margin. Civil aircraft regulators are allergic to storing fuel in the fuselage near the passengers for good reason.

[R0b0t1]

The containers for the hydrogen can be made to vent safely for a lot of impacts. Fiberglass, carbon fiber, or other composites.