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April 7, 2013

Hydrogen Fuel Advance

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Someday we may all be driving vehicles powered by clean-burning fuel made by bacteria. As this ScienCentral story explains, researchers have found a way to jolt bacteria into producing one of the cleanest fuels available-hydrogen.

Power from Apple Pie

Hydrogen may be the fuel that someday both frees us from our need for fossil fuels and still keeps us in the cars we love. When today's hydrogen-powered cars hit the road, instead of polluting the air, the only by-product is water. So, why aren't manufacturers churning out thousands of hydrogen cars?

There are several reasons, but one of the most difficult to solve is how to make large amounts of hydrogen. In order to produce hydrogen today, manufacturers still use large amounts of fossil fuel, which defeats the purpose.

One promising method being explored by researchers at Penn State University is coaxing bacteria into producing hydrogen from just about any organic matter. "We could have given them bananas and oranges and apple pie and they could turn that into hydrogen," says Penn State Environmental Engineer Bruce Logan. He adds that practically speaking the bacteria can also use things we don't eat, like garbage, sewage, or plant material. As Logan notes, "anything that in nature, biodegrades."

Researchers have been exploring microbial fuel cells as a possible alternative source of energy. A small fan in Logan's lab runs from electricity produced by one such fuel cell.

But Logan's goal with this project is not electricity, but hydrogen. He says the bacteria eat the biodegradable material, "and they break it down into protons and electrons and we boost the voltage in a specially designed fuel cell, which works kind of like a battery." With the new step of adding a small amount of voltage and changing the structure of the fuel cell, Logan was able to produce hydrogen.

It takes energy to make energy and no process can create more energy than you put in. In this case energy comes both from the electricity and from the biodegradable material. Writing in Proceedings of the National Academy of Sciences, Logan says this process is very efficient. He says if you count both the biodegradable material and the electricity, the efficiency is about 82 percent. However, he notes, "if we just look at the amount of electrical energy that we put in, we actually get out almost three times as much energy in the hydrogen as we put in the electrical energy."

This compares favorably with other alternative fuel sources such as ethanol or biodiesel. For example, University of Minnesota ecology professor David Tillman found that when you count the amount of energy used to grow, fertilize, harvest, transport and process corn for ethanol, the amount of energy created is quite small, only 25 percent.

Logan's research is in its early stages. He sees the next steps as taking two directions. "We want to prove this technology at a larger scale," says Logan. He adds that in the laboratory he wants, to "improve the efficiency of the process (and to) reduce the size of the reactor."

If the technology proves itself, Logan doesn't expect that cars will have little generators turning sewage into hydrogen. He adds, "It's not going to be 'Mister Fusion' from 'Back to the Future.'"

Instead, he foresees the possibility that communities would have centralized hydrogen-processing facilities. He says the processes is sufficiently complex that it will need a manufacturing facility capable of handing higher levels of technology.

This research was published in the Proceedings of the National Academy of Sciences Online Early Edition the week of November 12-16, 2007 and was funded by grants from the National Science Foundation and Air Products and Chemicals, Inc.

       email to a friend by Jack Penland

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