Biofuel cells to replace rechargeable batteries

Instead of using expensive metals to catalyse the power-producing reaction, biofuel cells use enzymes.  

SCIENTISTS AT the Saint Louis University have developed a new type of biofuel cell — a battery that runs on alcohol and enzymes — that could replace the rechargeable batteries in everything from laptops to Palm Pilots. Instead of plugging into a fixed power outlet and waiting, these new batteries can be charged instantly with a few millilitres of alcohol.

The new findings were presented today at the 225th national meeting of the American Chemical Society, the world's largest scientific society, in New Orleans.

Instead of using expensive metals to catalyse 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," says Shelley Minteer, an assistant professor of chemistry at Saint Louis University. Given the proper environment, an enzyme should last for long periods of time.

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 and her colleagues coated the electrodes with a polymer that has specially tailored micelles — pores in which the enzymes find an ideal `micro-environment' 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 says. "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 five square centimetres — about the size of a postage stamp. "We have tested probably 30-50 of the ethanol cells," Minteer says. They have successfully run their cells with vodka, gin, white wine and flat beer .

While consumer applications are still a few years off, "these results show the applicability of biofuel cell technology and help move the research from a purely academic endeavor to a more practical technology," Minteer says.