Hydrogen burns in pure oxygen to form water in the following reaction:

2H2 + O2 ---> 2H2O + 483 kJ

Therefore the energy density of hydrogen gas is 241.5 kJ/mol, or 9.874 kJ per Liter. The published density of liquid hydrogen is 0.07 g/mL, which translates into 70 moles per Liter. For combustion with oxygen the corresponding energy density of liquid hydrogen is therefore 8,452.5 kJ per Liter, or 120,750 kJ/kg.

The video provided on Millennium Cell's website stated that their solution contained:

75 percent water
20 percent sodium borohydride
5 percent sodium hydroxide

It is assumed that these proportions are based on mass of solute. So 100 grams of liquid solution would contain:

4.170 moles water
0.530 moles sodium borohydride
0.125 moles sodium hydroxide

These amounts of solute would create approximately 102.1 milliliters of solution. Since the alkalinity of sodium hydroxide stabilizes the solution, then the addition of a catalyst would cause the reaction:

Ruthenium
Catalyst
NaBH4 + 2H2O ----------> NaBO2 + 4H2

There is already excess water in the solution so the quantity of sodium borohydride is the limiting factor in how much hydrogen is produced. For each mole of NaBH4 the reaction yields four moles of hydrogen gas, or 4H2. This 100-gram sample solution should therefore yield 2.12 moles, or 4.24 grams of hydrogen gas.

At STP this amount of hydrogen will occupy 52.342 Liters volume. When burned in pure oxygen it will liberate 511.98 kJ of energy. This gives a energy density for sodium borohydride of 5014.5 kJ per Liter, or 5119.8 kJ/kg. So lets compare the final energy densities, in million Joules per kilogram, of Millennium Cell's "Hydrogen On Demand" fuel to other various fuels and electric batteries:

1. Nickel-cadmium battery = 158 kJ/kg
2. Silver-Zinc battery = 396 kJ/kg
3. Lead-acid battery = 792 kJ/kg
4. Sodium-sulfur battery = 792 kJ/kg
5. Lithium-Sulfur battery = 792 kJ/kg
6. Solid Iron-titanium hydride = 2,124 kJ/kg
7. Liquid Sodium borohydride = 5,120 kJ/kg (5014.5 kJ per Liter)
8. Solid Magnesium hydride = 8,280 kJ/kg
9. Liquid hydrogen = 120,750 kJ/kg (8,452.5 kJ per Liter)
10.Gasoline = 47,500 kJ/kg (34,561 kJ per Liter)

However the fuels will be used in different types of engines with different efficiencies. A gasoline engine has 20 percent efficiency, and a hydrogen fuel cell has 40 percent efficiency. Taking the most promising fuels and adjusting them for engine efficiency yields a better result. Fuels 1 thru 4 are to be used with a fuel cell, while gasoline is to be used in an internal combustion engine:

1. Solid Iron-titanium hydride = 850 kJ/kg
2. Liquid Sodium borohydride = 2,048 kJ/kg (2006 kJ per Liter)
3. Solid Magnesium hydride = 3,312 kJ/kg
4. Liquid hydrogen = 48,300 kJ/kg (3381 kJ per Liter)
5. Gasoline = 9,500 kJ/kg (6912 kJ per Liter)

I still like Millennium Cell's sodium borohydride fuel.