The benthic microbial fuel cell, advanced by U.S. Naval Research Laboratory scientist Dr. Lenny Tender, will undergo ocean testing as part of a multi-year effort to develop a continuously operated power source for ocean sensors.
Ocean sensors, now powered almost exclusively by man-made batteries, one day could be fueled by an energy source found in a most unlikely place — the bottom of the sea.
Dr. Lenny Tender, a microbial electrochemist at the U.S. Naval Research Laboratory (NRL) in Washington, D.C., has spent nearly two decades advancing the Benthic Microbial Fuel Cell that generates an indefinite supply of electricity using microorganisms residing on the ocean floor as its fuel and oxygen in the overlying water as its oxidant.
Now that Tender has proven the technology during demonstrations with small-scale fuel cells, which generated about one-tenth a watt of power under a variety of marine environments, he and his team plan to resume ocean testing — this time with a full-scale model that could power most oceanographic sensors.
“We’ve done dozens of field demonstrations powering all types of devices,” Tender said, referring to one such deployment where the benthic microbial fuel cell operated for nearly two years. “We’re ready to go back to the ocean. Our goal now is to demonstrate 1 watt of continuous power, which is more than enough to power conventional oceanographic instruments.”
Just as important, he said, will be its ease of deployment. The latest incarnation will be installed inside a “Hershey Kiss”-shaped mooring that can be easily lowered into the ocean from the side of a ship.
The need for an easily deployed fuel cell that creates an unlimited supply of energy to power a host of sensors cannot be overstated, he said. The U.S. Navy and many other organizations deploy thousands of battery-operated sensors each year to monitor everything from fish populations, water quality, and oil spills, to ocean salinity and temperature. However, batteries deplete their power and must be replaced — an expensive and time-consuming task that is not always possible under certain conditions.
Some envision the Navy and others eventually using the technology to replenish batteries on unmanned undersea vehicles or sensor networks that track ship traffic. The technology even offers significant applications for land-based operations. Tender is now expanding his research to include wastewater treatment, exploiting the same microbial processes that occur in the marine environment to generate power.
His technology offers an enticing solution to anyone who relies on battery-powered devices to gather marine-related data. It generates power using an inexhaustible supply of fuel. “Sediment and water is a ready-made battery,” Tender said. “What you’re lacking are the electrodes.”
Consequently, Tender’s technology includes two electrodes: the anode is sunk into the muck — a gigantic reservoir of fuel created over the millennia by decomposing plankton, plants, fish, and other sea organisms. The cathode hovers above in the oxygen-rich seawater.
But that’s only part of the story, Tender said.
Early in his research, he discovered an interesting chemical process that made the fuel cell virtually unstoppable. In a shoebox-sized aquarium, Tender sunk an anode into the sediment and the cathode in the overlying water. The set up produced a miniscule current. To his shock, however, the current did not diminish, as would be expected due to the depletion of the anode’s catalytic activity. It increased.
He removed the anode and found a microfilm growing on its surface. As it turned out, microbes had colonized the embedded anode where they had been dining on the sediment’s organic stew. As the microbes broke down the matter, they transferred electrons to the anode. The electrons then flowed from the anode as current to the cathode, where the electrons then reacted with oxygen in the water, thus liberating energy. In other words, the microbes were constantly rejuvenating the electrode reaction.
“The microbes act as a catalyst and they keep going,” Tender said. That discovery contributed to the establishment of a new field of study — microbial electrochemistry — and the formation of the International Society for Microbial Electrochemistry and Technology (ISMET), Tender said.
Since the discovery, Tender has tested a number of different designs under a variety of conditions and environments. He has dropped fuel cells off the coasts of California, Maine, New Jersey, and North Carolina, as well as in the Gulf of Mexico, the Adriatic Sea, and the Potomac River.
Under the new fuel-cell configuration that he plans to test, also under a variety of conditions, Tender will place the anode on the bottom of the “Hershey Kiss”-shaped mooring that measures roughly 6.5 feet in diameter and the cathode on the topside. He also will attach instruments that he plans to power with the expected 1 watt of power and include the ability to store energy, which will be used to charge a battery.
“What we want is to drop something off a ship in deep water and not worry that it will work or that its batteries have a limited lifespan,” Tender said. “This is a simple design.”
Lori J. Keesey is a freelance writer, who specializes in new technology development. She can be reached at Lori.J.Keesey@nasa.gov