Bacteria, Salt Water Make Hydrogen Fuel

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The 'hydrogen economy' requires a lot of things, but first is an easy and cheap supply of hydrogen. There are lots of ways to make it, but most of them don't produce large quantities quickly or inexpensively. 

Professor Bruce Logan, director of the Hydrogen to Energy Center at Penn State University, has found a way to change that. He used a process called reverse electrodialysis, combined with some ordinary bacteria to get hydrogen out of water by breaking up its molecules.

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Water — which is made of two atoms of hydrogen and one of oxygen — can be broken down with electricity. (This is a pretty common high school science experiment). The problem is that you need to pump a lot of energy into the water to break the molecules apart.

Logan thought there had to be a better way. He combined two methods of making electricity — one from microbial fuel cell research and the other from reverse electrodialysis.

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In a microbial fuel cell, bacteria eat organic molecules and during digestion, release electrons.

In a reverse electrodialysis setup, a chamber is separated by a stack of membranes that allow charged particles, or ions, to move in only one direction. Filling the chamber with salt water on one side and fresher water on the other causes ions to try and move to the fresher side. That movement creates a voltage. Adding more membranes increases the voltage, but at a certain point it becomes unwieldy.

By putting the bacteria in the side of the reverse electrodialysis chamber with the fresh water, and using only 11 membranes, Logan was able to generate enough voltage to generate hydrogen. Ordinarily he would need to generate about 0.414 volts. With this system, he can get .8 volts, nearly double. (The microbial part of the cell generates 0.3 volts and the RED system creates about 0.5.)

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Using seawater, some less salty wastewater with sewage or other organic matter in it and the bacteria, Logan's apparatus can produce about 1.6 cubic meters of hydrogen for every cubic meter of liquid through the system of chambers and membranes. Another bonus is that less energy goes into pumping the water — if anything, flow rates and pressure have to be kept relatively low so as not to damage the membranes. 

Making hydrogen cheaper is a necessity if hydrogen cars are to be a reality. Some car companies already make hydrogen-powered models. The state of Hawaii is already experimenting with hydrogen fuel systems. Producing cheaper, abundant hydrogen — especially from sewer water and seawater — is a big step in that direction.

Image: Bruce Logan, Penn State University.

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