Why does the hydrogen need to be liquid? Airships are weight not volume constrained, so you could probably just store it as gas. You could make it buoyancy neut

Why does the hydrogen need to be liquid? Airships are weight not volume constrained, so you could probably just store it as gas. You could make it buoyancy neutral by compressing it (at 13 atm it has the same density as air at 1 atm), or carrying oxygen as well (which would also make the fuel cells more efficient that just using hydrogen + air). In some ways hydrogen is an ideal fuel for airships, because although the energy density is very low, the specific energy is very high — much higher than batteries, and 2-3 times hydrocarbon fuels.