Electricity from silk cocoons?
Researchers in India say they have developed a prototype of an energy-harvesting device from the cocoons of a domesticated species of silk moth.
They hope to put the technology to practical use while also tackling waste materials from the silk processing industry.
The researchers found that the cocoon membranes of the mulberry silk moth Bombyx mori contain trace amounts of several elements such as sodium, chlorine, potassium, magnesium, sulphur, calcium and copper; as well as carbon, nitrogen and oxygen.
Wetting the cocoon makes the elements form mobile charge-carrying ions, producing an electric current across the cocoon membrane. The researchers used this current to light an LED.
They attached an aluminium electrode to the inner surface of a cocoon and a copper electrode to the outer surface, and exposed the cocoon to water vapour. Three such cocoons were connected in series to light an LED.
The researchers also charged a moist silk cocoon with a direct current source to see if it was capable of acting as a capacitor — a device that stores charge. They reported in Scientific Reports that it could power an LED for two to three minutes after the direct current was removed.
The researchers also looked at whether temperature affected the current the cocoon generated. They found that both voltage and current increased at higher temperatures of around 50 to 60 degrees Celsius because the resistance to current flow in the cocoon membrane decreased.
This shows that silk cocoons can be used to power electronic systems in "hot and humid conditions", says Sushil Kumar Singh, co-author of the paper and researcher at the Defense Research Development Organisation, India.
"Silk cocoon can act as a green, energy-harvesting device in iron ore industries, and nuclear power plants, where you find waste heat and a humid atmosphere," Singh tells SciDev.Net.
But James S. Brooks and Eden Steven, researchers at US-based Florida State University who have been working on spider silk's electrical properties, have reservations about the work.
"Silk would not generate electricity on its own," they tell SciDev.Net jointly in a joint e-mail. "Silk, in the absence of water, is an electrical insulator... The observed effects are very likely due to the wet electrochemistry between the aluminium and copper [electrodes] and the ions present in the cocoon."
Continue reading at ENN affiliate, SciDev.Net.
Silk cocoon image via Shutterstock.