They attribute their success to two things. First, they chose ethanol instead of methanol for their fuel. “A big advantage is that ethanol is not toxic like methanol, so it is easier to deal with,” said team leader and assistant professor of chemistry Shelley Minteer. “You can use any alcohol. You will be able to pour it straight out of the bottle and into your battery,” said team member Nick Akers, a graduate student. “We have run it on various types. It didn’t like carbonated beer and doesn’t seem fond of wine, but any other works fine.” Eventually, they hope that one to three drops of alcohol could power a cell phone for a month.
The other key to their success is the extremely stable environment they have created for their enzymes. They coated the biofuel cell’s electrodes with a polymer that contains tailored micelles, or pores, which provide an ideal microenvironment for the enzymes to thrive. Their biofuel cell has been producing a constant current for over two months now. “There’s no evidence that it is going to stop tomorrow. We don’t know yet how long it’s going to last. Could be six months,” Akers said.
The Saint Louis team is striving to increase their biofuel cell’s power density. Currently, their battery produces 2 milliwatts of power per effective square centimeter, whereas the average cell phone requires 500 milliwatts. They are also trying to design a battery that can fit today’s portables while producing the necessary power output. “It’s like a radiator in car,” Akers said. “It’s folded, and all those ridges and folds give it a high surface area so the effective surface area becomes tremendously huge. You can do this on a micro scale so that the effective surface area of the electrodes is enormous. This is what we are doing in the designing process.” Akers believes their team will have a working prototype in a year, and that the finished product will hit store shelves a year later.