Shelley Minteer and her colleagues at the St. Louis University (St. Louis, MO) have developed an enzyme-catalyzed battery that is suitable for powering cell phones and other portable devices. The key to the device is a new polymer that protects the fragile enzymes used to break down the ethanol fuel. Enzyme-based batteries have the potential to be cheaper than fuel cells that rely on expensive platinum or ruthenium catalysts. Enzymes are inexpensive and catalytically very active.
The researchers have used enzymes found in ethanol to strip off the hydrogen. However, 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. The typical approach to solving this problem has been to immobilize the enzymes by attaching them to the fuel cell's electrodes, but they still tend to decay too quickly to be useful. Minteer’s team coated the electrodes with a polymer that has specially tailored pores, which maintains a neutral pH, 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," reported Minteer. "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."
The cell is still too large for portable use. The group is currently working to shrink the technology by manipulating the polymer-enzyme matrix in order to increase its surface area further.
