Hydrogen best case density is ~ 2.5 kWh/kg, definitely not that great considering this is in its liquid form. To stay in that form, you need to cool them to ~ 2

Hydrogen best case density is ~ 2.5 kWh/kg, definitely not that great considering this is in its liquid form. To stay in that form, you need to cool them to ~ 20˚K, which is about -253°C. Also, because the molecules are so small, the tank needs to be almost perfect. Even the crystal structure of metals is eventually penetrated by hydrogen. Hydrogen has many sensible uses in the production of many goods, filling powerful electrical generators etc. It would be great if we could produce it economically in a renewable fashion. Actually, there are many carbon free fuels. It is hard for any to use as jet fuel. An example fuel that has much better properties than hydrogen is for instance sodium. Making a sodium fuel cell does not need any rare earth metals such as platinum, sodium is solid at room temperature, does not produce any fumes, better energy density than liquid hydrogen, the resulting NaOH sodium hydroxide can be recycled into sodium (with hydrogen as a byproduct) by the Castner process. Hard to say, if this could use the water vapor present in the atmosphere, if it did, you would also have to think about what to do with the caustic hydroxide solution. Probably, that would be neutralized quickly in the atmosphere but at ground level or above cities could "raise eyebrows" even though burning leaded petroleum in aviation still seems to be a thing...