Researchers at the Institute of Physical Chemistry in Poland have created an air-breathing biobattery that could one day provide long-lasting and safe power to pacemakers and other implants. In the words of the lead researcher, Dr Jönsson-Niedziółka, who has a suitably Frankensteinian name, “One of the most popular experiments in electrochemistry is to make a battery by sticking appropriately selected electrodes into a potato. We are doing something similar, the difference is that […] we’d rather replace the potato with… a human being.”
The Polish biobattery is based on the same, well-known zinc-air chemistry that is used by hearing aid batteries. In a normal zinc-air battery, zinc (the anode) is oxidized by the oxygen in air (it’s an air-breathable battery), releasing electrons that travel to the cathode, producing electricity. As with most batteries, zinc-air batteries usually have a fairly dull carbon/graphite cathode. This new battery, however, uses a special cathode, which the researchers have been working on for many years.
The cathode, which the Poles are calling a biocathode [PDF], is fashioned from a biological enzyme (bilirubin oxidase) surrounded by carbon nanotubes. The nanotube-enzyme mix is then encapsulated by a silicate gel and deposited on an oxygen-permeable membrane. It might sound fairly complex, but the researchers say that this biocathode is easy to construct.
In practice, once it is combined with an anode and electrolyte, these enzymes reduce the oxygen in air to produce a lot of power — 1.75 volts, for a minimum of one and a half weeks, and a maximum power density of 5.25mW cm−2 at 0.4V — a lot for a fuel cell of this type. The carbon nanotubes help transport the electrons, increasing the power output. The cell’s efficiency does decrease over time, probably because the enzyme loses its efficacy. Experimentally, the researchers have used four of these biobatteries connected serially to power a two-LED bicycle lamp (pictured right).
Ultimately, the Polish researchers have made a solid step towards batteries that can power implanted devices, sensors, or, for the body modders out there, light-emitting tattoos. Zinc-air batteries are desirable for implants because zinc isn’t particularly toxic — and, like glucose fuel cells, there’s a possibility that the Polish zinc-air battery can generate power from the oxygen in your blood, providing a near-infinite source of power (as long as those enzymes can be finagled into lasting a long time).
Like lithium- and sodium-air batteries, which are being eyed up by the likes of IBM for use in electric cars, zinc-air batteries might also find a use in large-scale energy generation — though, again, it remains to be seen whether the enzyme is up to the task.
Research paper: http://dx.doi.org/10.1016/j.jpowsour.2012.11.081 – “Efficient air-breathing biocathodes for zinc/oxygen batteries”