The concept of aluminum as a fuel is new to me, so can't really comment on that one with any certainty, but hydrogen is a joke. The energy density of liquid hydrogen is only 8.5 MJ/L (megajoules per liter). Compare to gasoline at 34.2 MJ/L. There's actually more hydrogen in gasoline than there is in LH2, per volume.

Although aluminum is 83.8 MJ/L, it's weight becomes an issue, as 'light' as it is. But, I'm concerned that an 'aluminum energy cycle' can't become viable unless it is introduced on a massive scale from the get go. I suspect the fixed energy costs to initiate the process are too high and would far offset the benefit, resulting in a net loss.

The 2nd Law of Thermodynamics can be a real beach, eh?

Brian