The energy you spend in daily activities, such as exercising, walking or even sitting and typing in front of the computer, will no longer be wasted, but converted to electrical energy for powering-up your cell phone, tablet, or other smart electronics through a promising wearable energy-harvesting device developed by City University of Hong Kong (CityU). 

With this novel device, the energy collected from your daily activities is expected to contribute 5 to 25% of the energy required to run the battery of a small portable electronic gadgets. The research has recently been published in the journal Advanced Functional Materials and has already drawn interest from potential industry partners.

The research team, led by Dr Walid Daoud, Associate Professor in CityU’s School of Energy and Environment, has combined two energy conversion concepts, namely piezoelectric and triboelectric effects, to create a hybrid system. It is a sandwich structure, whose surface has zinc oxide nanorods to maximise the effective electrification area. When mechanically compressed, the piezoelectric generator produces polarization charges, and the triboelectric generator produces triboelectric and electrostatic charges. The flow of these charges through an external circuit forms an electric current, which can be stored in the form of electrical energy.

Researchers on the team were able to develop the hybrid system after successfully unravelling the energy-conversion mechanisms of the individual generators and the combined effects.  

“We conducted this pioneer study to better understand the transduction mechanisms. These findings provide a foundation of knowledge to further enhance the conversion efficiency and energy output of hybrid generators. We found that the energy output can be increased by 50 to 60% owing to the zinc oxide nanorods,” said Dr Daoud.

Dr Daoud’s team is exploring the vast range of possibilities revealed by these crucial findings. For instance, a device could be fabricated using textiles to make it a part of your clothing. It could also be installed in a shoe sole, which would be one of the most efficient settings for harvesting the energy pulses produced by our movements. The energy generated could be transmitted wirelessly to charge a portable device.  

This promising technology has attracted the interest of a leading smart electronic company to apply it in its smart watches. 

“By virtue of its simple design and the wide range of materials it can be used with, the device is highly practical and the manufacturing cost is expected to be low,” added Dr Daoud.