MICROORGANISMS in the seafloor may soon be producing an unlimited supply of electricity to power equipment such as sensors and sonar beacons. It comes from a fuel cell developed with funding from the US Department of Defense, which taps into a natural voltage gradient at the bottom of the ocean.
Bugs living in seawater, or on the top layer of seafloor sediments, use oxygen to break down organic matter, releasing energy as they go. Those that live further down where there is no oxygen, have to rely on other chemicals, such as nitrates and sulphates.
These different reactions create an electrical potential difference, just like the voltage between opposite electrodes of a battery. Clare Reimers at Oregon State University in Corvallis and Leonard Tender of the Naval Research Laboratory in Washington DC decided to harness this in a fuel cell, to provide an endless source of electrical energy.
Their lab prototype uses a negatively charged electrode buried in about 10 centimetres of sediment with a positively charged partner just above the surface.
When the electrodes are connected, they generate 003 watts per square metre, enough power to run a small light emitting diode. And the tireless work of microbes means that the power supply should be never-ending. "That is incredibly cool," says Deborah Bronk, a microbiologist at the University of Georgia in Athens.
Reimers is experimenting to increase the cell's power. In the spring, divers will install similar fuel cells in real ocean sediments. Later versions could be designed to bury themselves.