Researchers at the Naval Undersea Warfare Center in Newport, R.I. (USA), recently conducted a continuous 37-hour demonstration of a high-energy electric power source to propel unmanned undersea vehicles. The power source, a semi-fuel cell, which combines features of a fuel cell and a standard battery, will provide a cheaper, safer source of power with four times as much energy as current silver-zinc batteries.
In the Navy of the future, unmanned undersea vehicles will carry out a range of tasks, including shallow-water surveillance, information gathering and mine detection. A useful energy source for these vehicles must permit high voltages, have a large energy storage capacity, and safely and reliably deliver the stored energy over extended discharge times. The energy source must also be relatively inexpensive, environmentally safe, and capable of a long shelf life.
A fuel cell is essentially an "electrochemical engine" that carries all of its reactants, typically hydrogen and oxygen, in storage tanks external to the fuel cell itself. Batteries, on the other hand, contain all of their energetic materials within the power producing block or electrochemical cell. The semi-fuel cell is a hybrid of the two. The reducing agent, or anode, is aluminum or magnesium metal that is permanently contained inside the cell where it undergoes electrochemical oxidation with hydrogen peroxide. The liquid hydrogen peroxide is carried external to the electrochemical cell and is fed into the cell as power is demanded. And the battery fluid? It's seawater; something that's available in abundance to undersea vehicles. The ions in seawater provide the conductivity needed to carry electrical current in the operating semi-fuel cell.
More information: Office of Naval Research, Diane Banegas