Researchers at the Oxford University have developed a pioneering "biofuel cell" that produces electricity from ordinary air spiced with small amounts of hydrogen and offers significant potential as an inexpensive and renewable alternative to the costly platinum-based fuel cells that have dominated discussion about the "hydrogen economy" of the future.

Hydrogen fuel-cell technology sounds almost too good to be true. You combine cheap and plentiful hydrogen and oxygen gas, the fuel cell generates electricity and the by-product is simply water. But it's a little more involved.

The key is a proton exchange membrane, or PEM, containing platinum. The platinum acts as a catalyst that separates electrons from the hydrogen gas atoms. The free electrons are gathered as current and the positively charged hydrogen ions pass through the membrane where they readily combine with oxygen atoms to form water. But if the hydrogen gas contains impurities, such as water vapor or carbon monoxide, it can damage the fuel cell's separation membrane, dropping efficiency or stopping the process altogether.

Another disadvantage is the fact that as a precious metal, platinum is in short supply, raising questions about the sustainability of platinum-based fuel cell technology. Platinum is more costly than gold, with recent prices topping $1,000 per ounce

Pure hydrogen is also hard to come by, so the team built the biofuel cell with hydrogenases - enzymes from naturally occurring bacteria that use or oxidize hydrogen in their metabolism.

The cell consists of two electrodes coated with the enzymes placed inside a container of ordinary air with 3 percent added hydrogen and uses enzymes from Ralstonia metallidurans (R. metallidurans), an ancient bacterium believed to have been one of the first forms of life on Earth. It evolved 2.5 billion years ago, when there was no oxygen in Earth's atmosphere, and survived by metabolizing hydrogen.

Fraser Armstrong, Ph.D. at the Oxford University, pointed out that naturally occurring hydrogenase enzymes can be produced at lower cost, with carbon-monoxide poisoning not being a problem. Since the hydrogenases are chemically selective and tolerant, they work in mixtures of hydrogen and oxygen, avoiding the need for expensive fuel-separation membranes required in other types of fuel cells.

Hydrogenases also work at about the same rate as platinum-based catalysts, but in the current version of the cell the only disadvantage is the fact that the enzyme is not attached tightly to the electrode and the cell runs for only about two days.

Now, the researchers are investigating the use of enzymes from other organisms for more practical results that could be implemented in future car manufacturing processes.