In the underwater world of Unmanned Undersea Vehicles (UUVs), propulsion of these mobile laboratories, which often resemble a torpedo, is usually provided by electric motors powered by batteries. While battery technology has improved over the years e.g. lithium-ion, UUV range and power is restricted by battery capacity.
Caption: The US Navy's Seahorse UUV, is reported to be the first application of the aluminum - steam hydrogen generating propulsion system. Image credit: US Navy
In an attempt to improve the range of UUVs, the alternative energy company AlumiFuel Power Inc, (API) researching on behalf of the US Navy, into possible use of hydrogen generation using steam and aluminum . The advantages of hydrogen as a fuel in combustion engines as well a fuel cells have been well documented and its production by electrolysis although straightforward requires special facilities for its transport and storage. Another method to produce the gas is using aluminum and steam (water) in a controlled exothermic reaction to produce hydrogen gas, water and aluminum oxide. The latter can be recycled into aluminum and reused. For the chemists, the equation is: 2Al + 3H2O = Al2O3 + 3H2. Superheated steam at 390 - 570 deg F (200-300 deg C) is required to remove the protective oxide on the aluminum surface and act on the clean aluminum. The aluminum is basically oxidised by the oxygen in the steam and the "stripped" hydrogen emitted as a free gas. The rate of hydrogen emitted is simply controlled by the supply of steam reacting with the aluminum. It is not necessary to cool or compress the hydrogen gas if it can be fed straight to a fuel cell or combustion engine.
Caption: Examples of aluminium canisters produced by API for use in their commercially available land based hydrogen generators. Image credit: AlumiFuel Power Inc