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Living fuel cells

​Bacteria contain astonishing enzymes that could inspire scientists in the fabrication of fuel cells. Such is the case for researchers from the IBS, who have just determined the crystallographic structure and mechanism of action for an enzyme from Escherichia coli.

Published on 28 February 2013

A hydrogen fuel cell involves the creation of an electric current between two electrodes. At one electrode, hydrogen is oxidized by losing two electrons. These electrons migrate to the other electrode to participate in the reduction of oxygen, and create an electric current.

Oxidation reaction: H2 → 2H++ 2e-

Reduction reaction: 4H++ 4e- + O2 → 2 H2O

Conventional devices, which use a proton exchange membrane and a platinum catalyst, are still expensive (for more information: Production d’hydrogène: si le cobalt remplaçait le platine… ). A team from the IBS has shown that certain bacterial enzymes are very effective at oxidizing hydrogen from the air and sending the electrons to the catalytic site where the oxygen will be reduced. This biofuel cell naturally performs within Escherichia coli, thanks to a hydrogenase that has a series of aggregates composed of iron and sulfur in a particular geometry (Fe4S3) forming a link between its surface and the catalytic site.

Crystallography studies and calculations made in collaboration with the CEA-Inac and Oxford University show how this tiny biological power station functions, which is typically capable of powering a watch for several hours. Unlike classic hydrogenases that are damaged by atmospheric oxygen, this enzyme is able to send (thanks to the Fe4S3 aggregate) not one, but two electrons from its surface to the catalytic site and to rapidly reduce the oxygen, producing water. Due to the speed of this reaction, the oxygen does not have time to damage the enzyme’s catalytic site. This “super oxidation” ability could ultimately inspire the industry in producing biomimetic fuel cells.

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