Collecting data on the ocean floor may soon get a lot easier, thanks to a fuel cell that runs off organic detritus in the mud at the bottom of the sea. Instruments powered by the new device could operate forever (at least in principle) without the hassle of swapping batteries.
Scientists have known about the untapped potential at the ocean bottom for decades. Mud-loving microbes convert organic matter into electron-rich molecules, building up an electric potential between the soil and the electron-poor water above. Earlier this year, a team of researchers reported that electrodes in laboratory aquaria--after being colonized by a certain type of bacteria--carry a flow of electrons that can power a pocket calculator (Science, 18 January, p. 483).
Now, some of these researchers have plopped the device into shallow harbor waters off Oregon and New Jersey. Led by Leonard Tender of the Naval Research Laboratory in Washington, D.C., and Clare Reimers of Oregon State University in Newport, the team built electrodes from two graphite disks, each about 14 centimeters in diameter and drilled with small holes to increase the surface area for chemical reactions. One disk they buried in sediment, the other they placed in the water above. Bacteria growing on the buried plate pumped electrons into the electrode as they consumed organic matter (which is continually replenished by falling detritus from above). Oxygen molecules in the water plucked available electrons off the upper electrode, creating a current that provided about 0.02 milliwatts of power--enough to power simple ocean sensors, the researchers report in the 1 July issue of Nature Biotechnology.
Engineer Paul Chandler of the Monterey Bay Aquarium Research Institute in California, who designs oceanographic equipment, says that sensors are often not placed in remote areas because of the cost of replacing batteries, and this discovery might expand the areas that scientists can study. "The need is there, the energy resource is out there, and it looks like we can learn how to exploit it," he says.