NPR : China Spans the Globe Searching for New Energy Sources

A hydrogen fuel cell that uses enzymes instead of expensive metal catalysts to drive chemical reactions has been developed by UK researchers.

Enzyme-powered fuel cells could be smaller, simpler and cheaper to make than conventional ones, the researchers claim. They have already powered a digital watch using their invention.

Hydrogen fuel cells are an attractive alternative to conventional batteries because they require only hydrogen and oxygen to produce electricity, and generate only water as a waste product.

Conventional fuel cells work in two stages. Hydrogen is first split into protons and electrons before being combined with oxygen to make water. The reactions take place on separate electrodes, forcing electrons to travel through a circuit in between, generating an electrical current. But these reactions normally rely on electrodes incorporating expensive metal catalysts, such as platinum.

Researchers from Oxford University in the UK used two enzymes, one harvested from bacteria and the other from fungus, to catalyse the same chemical reactions. Each electrode is coated in one of the two enzymes. The bacterial enzymes break down hydrogen as part of their natural metabolism, and the fungal enzymes naturally combine hydrogen with oxygen – usually to break down wood.
Mixed fuel

As the enzymes are specially geared towards driving these two reactions, they can be used to make a more compact fuel cell, that allow small amounts of both fuel to mix together. "With platinum electrodes, a special membrane has to be used to keep the two fuels separate, or you'd get no power at all," explains Kylie Vincent from Oxford University. "If you have very specific catalysts like enzymes, you don't need a membrane."

This should cut the cost of making a fuel cell, Vincent says. "The enzymes are also completely biodegradable," she adds.

The team has so far developed a simple prototype – a glass tank containing two electrodes, each coated with one of the enzymes. Adding a few per cent of hydrogen to the air inside the tank triggers the enzymes into action, and a small current is generated. The fuel cell can so far produce about 700 millivolts, enough to power a digital watch.

Paul Allen, an energy expert from the Centre for Alternative Technology, in Wales, UK, says the cell could make an excellent alternative to the batteries used in portable gadgets. "The batteries used in watches and cameras are energy intensive to produce and contain heavy metals, making them difficult to dispose of," he told New Scientist. "A cost-effective rechargeable alternative would be useful."

But Allen notes that energy is still needed to produce the hydrogen required. "We must remember that fuel cells are energy stores not energy generators," he says. "Unless we develop renewable energy-generating capacity in the first place, there will still be a net energy shortfall in the future."
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