Hydrogen, being the smallest atom, tends to leak. For this and energy density reasons, the hydrogen must be cryogenically stored, at low temperature and high p

Hydrogen, being the smallest atom, tends to leak. For this and energy density reasons, the hydrogen must be cryogenically stored, at low temperature and high pressure. I don't think that nut has been cracked. Creating pure hydrogen cheaply and without CO2 emissions from the reformation process is also an unsolved problem, I think.