Sony Corp. announced that it prototyped a bio battery that is capable of generating electricity by breaking down glucose with enzymes and succeeded in playing back music with the battery.
The NW-E407 memory-type Walkman and passive speakers (driven by the Walkman's power supply) were powered by the bio battery. The main specifications of the bio battery (cell) are its maximum output of approximately 50 mW, dimensions of 39 mm (W) x 39 mm (H) x 39mm (D) and its substantial cell capacity of about 40 cc (excluding the chassis).
According to Sony, the prototype unit has the world's highest output for a passive bio battery, which absorbs glucose, oxygen and other reactants in the cell from the electrode by natural diffusion (based on Sony research as of Aug. 23, 2007). Four cells were used in the demonstration.
This bio battery using glucose has an anode with immobilized glucose-digesting enzymes and electronic conduction materials and a cathode consisting of an immobilized oxygen-reducing enzyme and electronic conduction materials. The battery is composed of these electrodes and a separator sandwiched between them.
The mechanism of generation is as follows: First, the glucose solution taken in from the anode is oxidatively decomposed by enzymes to generate electrons and hydrogen ions. More specifically, this reaction is expressed by the following formula: Glucose -> Gluconolactone + 2 H+ + 2 e-
The hydrogen ions obtained migrate to the cathode through the separator. The electrons also move to the cathode via the external circuit. At the cathode, oxygen absorbed from the air reacts with the hydrogen ions and electrons from the anode under a catalyst to produce water.
More specifically, a reduction reaction expressed by the following formula takes place: (1/2) O2 + 2 H+ + 2 e- -> H2O
Through this process of electrochemical reaction, the battery generates electricity when the electrons pass through the outer circuit.
In order to increase the output of the battery, Sony mainly focused on the following three points: (1) Development of technology to densely immobilize the enzymes and electronic conduction materials (mediator for conduction) at the anode while maintaining the activity of the enzymes; (2) Development of technology to optimally retain water content at the cathode so that the oxygen required for the reaction is effectively absorbed; and (3) Optimization of the catalyst.
In regard to item (1), two polymers having opposite charges were utilized as the substance that acts as a "glue" to immobilize the enzymes and electronic conduction materials. These components are densely attached on the electrode by means of the electrostatic interaction between the two polymers.
According to Sony, the efficiency of extracting electrons from the glucose decomposition is significantly improved by optimizing the ionic balance at the time of immobilization and the process of producing the membrane electrodes with immobilized enzymes and electronic conduction materials.
With respect to item (2), porous carbon bearing the immobilized enzyme and electronic conduction material is used as the cathode. In addition, cellophane is used for the separator. Furthermore, the cathode is reportedly maintained at an appropriate water level by the optimization of the structure and the process of the cathode and separator.
Concerning item (3), the concentration of the phosphate buffer is increased from the commonly-used level, about 0.1 M, to 1.0 M. Sony reportedly discovered that the activity of enzymes immobilized on the electrode surface can be effectively maintained by increasing the concentration level and enhanced the power generation characteristics based on this finding.
The following substances and materials are used in the prototype battery cell: Glucose dehydrogenase and diaphorase for anode enzymes; bilirubin oxidase as a cathode enzyme; vitamin K3 and cofactor reduced nicotinamide adenine dinucleotide (NADH) for anode electronic conduction materials and potassium ferricyanide for a cathode electronic conduction material.
Porous carbon, titanium mesh and cellophane are used for the electrodes, current collector and separator, respectively. The glucose solution is a mixture of a glucose water solution (0.4 M) and a sodium phosphate buffer (1 M, pH 7.0).
Nikkei Electronics |
Nikkei Monozukuri |
Nikkei Automotive Technology |
|---|---|---|
 |
 |
 |
| The magazine for electronics designers and managers. | Design You Won't Regret - How to Reduce the Risk of Accidents | The comprehensive automotive technology magazine. |
Copyright © 1995-2010 Nikkei Business Publications, Inc. All rights reserved.
All editorial content and graphics on this Web site may not be reproduced in whole or in part without the express permission of the copyright owner.
