An enzyme-catalysed battery has been created that could one day run cell phones and laptop computers on shots of vodka.

The key to the device is a new polymer that protects the fragile enzymes used to break down the ethanol fuel, scientists told the American Chemical Society's annual meeting in New Orleans on Monday.

Enzyme-based batteries have the potential to be cheaper than fuel cells that rely on expensive platinum or ruthenium catalysts. "It sounds great," says Bob Hockaday, founder of the company Energy Related Devices and designer of a methanol-powered battery. "Enzymes are inexpensive and catalytically very active."

Fuel cells work by converting into electricity the energy released when oxygen and hydrogen react to produce water. Pure hydrogen is an explosive gas and difficult to store, so fuel cells often use a chemical source. Ethanol is used in Minteer's cell, and the enzymes strip off the hydrogen.

But the enzymes are sensitive to slight changes in pH and temperature and can rapidly degrade and become inactive. Until now no bio-battery had enzymes that lasted for more than a few days.

Specially tailored pores

The typical approach to solving this problem has been to immobilise the enzymes by attaching them to the fuel cell's electrodes, but they still tend to decay too quickly to be useful.

Shelley Minteer and her colleagues at St Louis University in Missouri coated the electrodes with a polymer that has specially tailored pores. These maintain a neutral pH, while being small enough to trap the enzymes yet big enough to let the alcohol pass through. "The enzymes have lasted over two months now and they are still functioning," she says.

Toshiba has just unveiled its first miniature methanol-powered fuel cell, which promises to keep laptops running for five hours between re-charging. But Minteer says: "The main advantage of ethanol over methanol is that it is simply more readily available. We have actually run our cells off vodka and gin."

Furthermore, ethanol is more productive with the enzymes used by Minteer's team and is less toxic. Their bio-batteries have power densities 32 times greater than those of other groups, they claim.

However, unlike the Toshiba prototype, the cell is still too large for portable use. The group is currently working to shrink the technology, perhaps by tweaking the polymer-enzyme matrix in order to increase its surface area further.

What are students drinking?

The survey results show that students are drinking the following types of alcoholic drinks:

The popularity of premixed drinks has increased among both males and females at the expense of beer for males and straight spirits for females.

There's a thin line that makes the difference

Craig