Green power may get greener with bacteria fuel cells

Sept. 20, 2011 - Jacob P. Koshy - livemint.com

A bucket of water and a handful of bacteria could be all that is needed to produce pure hydrogen to power the green engines of tomorrow, according to research by a team of US scientists.

A paper in Monday’s edition of the Proceedings of the National Academy of Sciences, a peer-reviewed journal, describes a method of constructing what are known as microbial fuel cells (MFCs). These cells are similar to regular batteries that consist of electrodes and an electrolyte, and which convert chemical energy into electricity.

MFCs are shaped like jewellery boxes and have all the oxygen contained drained out of them. Instead of chemicals such as lead, an army of bacteria masquerade as the electrolyte and supply the necessary voltage to produce electricity. This they do by excreting oxygen (derived from waste water in the box) that in turn releases electrons that attach to the cell’s electrodes.

“By adding a small amount of voltage (0.25 volt) to that produced by bacteria at the anode (where electrons collect) in an MFC, and by not using oxygen at the cathode, you can produce pure hydrogen gas at the cathode,” Bruce Logan, one of the authors and a professor at the Penn State University in Pennsylvania said over the telephone.

Hydrogen has emerged as one of the clean fuels that could allay concerns over climate change and rising fossil fuel costs. Although abundant in nature in combination, isolating it in sufficient quantities makes it an expensive energy option.

The voltage produced by the bacteria alone is too little to produce enough oxygen. To supplement that and generate hydrogen viably, the researchers made another series of cells made up of alternating layers of fresh water, sea water and separated by membranes.

“There’s a natural electric gradient that exists between saline and fresh water. When you connect several in series, you can get sufficient electricity,” said Vijayamohanan Pillai, director, Central Electrochemical Research Institute, Karaikudi, Tamil Nadu, who works on hydrogen fuel cells and has read Logan’s research paper.

In the paper, Logan and his co-authors said the hydrogen produced was a self-sustaining process viable enough to be scaled up.

“We still have to use platinum catalysts, but the amount of energy required to keep the process going was negligible,” he said in his research paper.

To be sure, it could take time for the new technique to become technologically and commercially viable to produce hydrogen in sufficient quantities, but Pillai said the attempts was a “fascinating step forward”.

At present, hydrogen doesn’t exist in isolation and is found hitched to carbon or oxygen, as biogas (or other hydrocarbons) or water. Isolating this bound hydrogen in enough quantities to store in fuel-storage devices, such as hydrogen cylinders, is what makes it expensive as a fuel.

In 2007, the Union government unveiled a hydrogen economy plan that envisages a million hydrogen-fuelled vehicles on India’s roads by 2020.

Pillai said that unless cheaper catalysts were found, he would remain a sceptic of Logan’s process.

“It’s an extremely innovative process of combining two different concepts. However, I’m not sure how scalable this is,” Pillai said. “It might be hard to practically get huge quantities of sea and freshwater, and we still don’t know if the microbes can be cultivated efficiently.”

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