Researchers at Saint Louis University have developed a new type of biofuel cell — a battery that runs off of alcohol and enzymes — that could replace the rechargeable batteries in everything from laptops to handhelds. Instead of plugging into a fixed power outlet and waiting, these new batteries can be charged instantly with a few milliliters of alcohol.
Biofuel cells have been studied for nearly half a century, but the technology has not advanced 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,” says Shelley Minteer, Ph.D., an assistant professor of chemistry at Saint Louis University who presented the research. “Given the proper environment, an enzyme should last for long periods of time. It is creating this environment in a fuel cell that researchers have struggled with for years,” Dr. Minteer says.
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. Dr. 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,” Dr. 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.
Dr. Minteer and her colleagues are focusing on small-scale applications, with the preliminary fuel cells being no bigger than five square centimeters — about the size of a postage stamp. “We’ve tested probably 30 to 50 of the ethanol cells,” she said. They have successfully run their cells with vodka, gin, white wine, and flat beer (“The fuel cell didn’t like the carbonation,” according to Dr. Minteer).
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.
The new findings were presented late last week at the 225th national meeting of the American Chemical Society, the world’s largest scientific society, in New Orleans.