A Quick Swipe at "Free" Hydrogen

I am busy with my thesis and marking at the moment but rather than issue corrections to my transport posts I just wanted to take a quick swipe at some specious hydrogen production claims.

A company called Alternate Energy Corporation claims to have some process that reacts water with metals to produce hydrogen gas. A quick browse of their website should set off alarm bells for anyone -- the distinct lack of any details on their system for example. Over at theWatt.com we've found some references to systems that burn aluminium to produce hydrogen. Aluminium won't react with water; you must introduce some acid or base to make the process run. Still, let's just imagine that we have the following irreversible reaction with zero enthalpy.

2 Al + 3H₂O → Al₂O₃ + 3 H₂

Given that you input 2 moles of Al for 6 moles of H it would require 9 kg of Aluminium to produce 1 kg of hydrogen. But the manufacture of aluminium is extremely energy intensive!!! Running the Aluminum Association's numbers I come up with 147.7 MJ/kg. This means you need 1329.3 MJ to produce one kilogram of hydrogen with an energy content of 142 MJ. This gives me an ERR of about 10 %. Whee.

If I ran a similarly fictitious reaction with iron I would need 18.6 kg of iron to make a kilogram of hydrogen. You can guess where this is going.

Now if we just burned the aluminium with oxygen in air... (we would have rocket fuel)