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鈥檚 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. 鈥淚t sounds great,鈥� says Bob Hockaday, founder of the company Energy Related Devices and designer of a methanol-powered battery. 鈥淓nzymes are inexpensive and catalytically very active.鈥�
Advertisement
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鈥檚 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鈥檚 electrodes, but they still tend to decay too quickly to be useful.
So 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.
鈥淭he enzymes have lasted over two months now and they are still functioning,鈥� she says. Thanks to the polymer, the new bio-batteries have power densities 32 times greater than those of other groups, the team claim.
Toshiba has just unveiled its first miniature fuel cell, which uses a metal catalyst and runs on methanol. Minteer says: 鈥淭he main advantage of ethanol over methanol is that it is simply more readily available. We have actually run our cells off vodka and gin.鈥� Ethanol is also less toxic and, with the enzymes used in Minteer鈥檚 bio-batteries, more productive.
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.