Sony Corp presented a bio battery that generates electricity by decomposing glucose using an enzyme at the International Hydrogen & Fuel Cell Expo (FC Expo 2009) taking place from Feb 25 to 27.
When supplied with Coke, it generated power and rotated a fan attached to a motor.
The bio battery decomposes glucose using an enzyme at the negative electrode and generates power by extracting electrons and hydrogen ions from it. Absorbing oxygen in the air at the positive electrode, the battery generates water through a reductive reaction of electrons and hydrogen ions.
This time, Sony doubled the battery's output density per unit volume achieved by the previous model, which was announced in August 2007, to 2.5mW/cc (See related article).
The company made two improvements to enhance the output density. First, it changed the electron-conductive material used for the negative electrode. By using a material that can lower the overvoltage needed to transfer electrons, the reaction at the negative electrode advances faster than before, according to the company.
Second, for a liquid solution used as a hydrogen ion conductor, Sony employed a solution whose pH does not change much. As a result, the response speed increased because the new solution stabilizes the hydrogen ion supply to the positive electrode, according to the company.
As the output density per unit volume was doubled, it became possible to play music with its Walkman portable music player and a set of passive speakers (which are powered by the Walkman) using three bio batteries, fewer than the four required with the previous bio battery. Compared with the previous 50mW/40cc model, the new 70mW/28cc bio battery has about twice as high output density.