...or they may soon belly up to the bar

InTech, May 2003

St. Louis, Mo.-A new type of biofuel cell, a battery that runs off of alcohol and enzymes, could replace rechargeable batteries in everything from laptops to personal digital assistants.

Instead of plugging in to a fixed power outlet and waiting, these new batteries can charge instantly with a few milliliters of alcohol.

Biofuel cell technology has not advanced over the past half-century to the point of practical use. Instead of using expensive metals to catalyze the power-producing reaction, these cells use enzymes-molecules found in all living things that speed up the body's chemical processes.

"The only items consumed in a biofuel cell are the fuel and oxygen from the air," said Shelley Minteer, Ph.D., an assistant professor of chemistry at Saint Louis University." Given the proper environment, an enzyme should last for long periods oftime. It is creating this environment in a fuel cell that researchers have struggled with for years," Minteer said.

Enzymes are extremely sensitive to changes in pH and temperature, and even slight departures from ideal conditions can lead to inactivation of the enzymes, producing a short supply of power.

The typical approach to overcoming this barrier has been to immobilize the enzymes by attaching them to the 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 micelles-pores in which the enzymes find an ideal "microenvironment" in which to thrive.

"The enzyme has everything it needs to function for a very long period of time instead of denaturing like it normally would," Minteer said." Other biofuel cell studies have had lifetimes of a few days; our technique allows for enzyme activity over several weeks with no significant power decay. With proper optimization, these biofuel cells could last up to a month without recharging."

Most other biofuel cells have used methanol as a fuel, but the researchers chose ethanol because it supports more enzyme activity. Ethanol is abundant and cheap to make, relying on the well-established corn industry for its production. It is also far less volatile than hydrogen, which has seen a great deal of interest as a potential alternative fuel for automobiles.

Minteer and her colleagues are focusing on small-scale applications, with the preliminary fuel cells being no bigger than 5 square centimeters-about the size of a postage stamp. "We've tested probably 30 to 50 of the ethanol cells," Minteer said. They have successfully run their cells with vodka, gin, white wine, and flat beer.