For hundreds of millions of years, plankton - those tiny drifting sea creatures found throughout the ocean - have been raining unceasingly on the sea floor as individuals die. There they've been deposited as organic (reduced carbon) matter in the sediment.
This organic matter is a rich and practically inexhaustible source of energy for animals and microorganisms that normally live at the bottom of the sea. Research jointly funded by the Office of Naval Research and the Defense Advanced Research Projects Agency (DARPA) is trying to harness just a small portion of this energy to power up small remote instruments.
ONR's oceanic fuel cell is called OSCAR (Ocean Sediment Carbon Aerobic Reactor). Organic matter in the sediment serves as the fuel which is connected to dissolved oxygen in the sea water by electrodes, allowing electrons to flow in the same manner as a conventional fuel cell. Microorganisms that naturally inhabit the sediment and sea water speed up the electron flow.
Early versions of OSCAR in place off the New Jersey and Oregon coasts are generating about 50 milliwatts per square meter of electrode at about 0.7 volts, about the power required for a small calculator, say the researchers from the Naval Research Laboratory, Oregon State University and the University of Massachusetts.
"Obviously, the bigger and more efficient the fuel cell electrodes are, the more power you'll get," explains Dr. Harold Bright, Office of Naval Research program manager for OSCAR. "OSCAR's unique advantage, compared to state-of-the-art sea batteries, is that it can produce small levels of power continuously and indefinitely. The day may come when we'll be able to use future versions of OSCAR to power ocean monitoring instruments such as ocean current meters and temperature and salinity probes. As it is now, ships have to go out every year or so to replace their sea batteries."