About 200 years ago, Michael Faraday discovered the fundamental principles of the electromagnetic induction effect. Most EMGs in our daily life work on this principle; in which an electric current is induced within a conductor exposed to a varying magnetic field. Through this they convert mechanical energy into electrical energy. There are various forms of mechanical energy for driving a generator, including heat engines, hydropower, wind power and nuclear power.

Towards triboelectric generation

Two years ago, Zhong Lin Wang of the Georgia Institute of Technology and his research team demonstrated an alternative device based on the triboelectric effect. Based on rubbing or touching two different materials together, the TEG works through a conjucation of triboelectrification and electrostatic induction to convert mechanical energy into electricity. Since their first publication on the TEG in 2012, Wang and his group have increased the power output density by a factor of 100,000. They have found that the volume power density reaches more than 400 kilowatts per cubic metre at an efficiency of more than 50 percent. The TEG can now instantaneously drive hundreds of light-emitting diodes (LEDs) and charge a lithium ion battery.

Complementary strengths

Now, a team led by Wang and comprising Fengru Fan and colleagues at the Beijing Institute of Nanoenergy and Nanosystems, Chinese Academy of Sciences, has shown that the power output performances of the EMG and the TEG have a special complementary relationship. Compared to the traditional EMG that produces a high output current but low voltage, the TEG has different output characteristics of low output current but high output voltage. In testing, the output performance of the TEG is close to or even better than the traditional EMG in small devices. It is expected that the TEG may be one of the preferred ways for large-scale energy harvesting in the environment, such as from wind and ocean wave energy.

The two kinds of generators were then integrated into a single device, which can be fixed on an automobile tyre to harvest mechanical energy during the rotation process. The further design of more complex structures can improve the output performance and broaden the scope of applications for the energy harvesters.

Full details can be found in the journal Nanotechnology 25 135402.

Further reading

Piezophototronics makes highly sensitive skin-like sensor (Aug 2013)
Power cell generates and stores energy in one step (Aug 2012)
Nanotechnology Discussions podcasts: Nanotechnology in tackling energy issues