From the pocket computers we call smartphones, to the booming tablet market, to handheld devices that display 3D imagery without glasses, just about every cutting-edge, consumer-grade technology ends up in mobile devices. Perhaps the biggest issue portables face, though, isn’t the ability to house complicated tech but to simply maintain a charge. However, a team of scientists has developed a portable nanogenerator that is capable of partially charging a lithium-ion battery using ambient energy as a power source.

The team of scientists composed of Sihong Wang, Ya Yang, Yan Zhang, and Zhon Lin Wang, dubbed the device “PENG,” which stands for pyroelectric nanogenerator. PENG gathers thermal energy through the use of the pyroelectric effect, basically how small changes in temperature have electric potential. Essentially, the nanogenerator harvests unused, potential energy from its surroundings and puts it to use.

Zhong Lin Wang says that released heat is a rich source of energy that doesn’t have to be wasted, and noted that in 2010, “more than 50 percent of the energy generated from all sources in the US was lost mainly in the form of wasted heat.”

Up until now, pyroelectric nanogenerators have only managed output voltages less than 0.1V, with a current below 1nA. However, the scientists’ new work with the PENG, building one out of a thin film of lead zirconate titante (PZT), managed a maximum output of 22V, with a peak current of 430 nA. With these new peak numbers one output pulse from PENG could power a small LCD for over one minute.

In order to put PENG to the test, the team applied its energy-harvesting ability to a lithium-ion battery. Over the course of three hours, the team noted that they managed to charge the battery at voltages ranging from 650mV up to 810mV. The team used the stored electricity to power a green LED for a few seconds. Though that is lightyears away from charging a 3.8V (or 3800mV) iPhone 5 battery in a reasonable amount of time, any practical application is a good one. (For reference, the iPhone 5’s battery has a capacity of 1440mAh and operates at 3.8V.)

Before an attempt to charge bigger devices can be made, the team must first figure out how to increase the PENG’s current. A standard USB charger has an output of 5V, and the new PENG managed a maximum output of 22V, but the current is still too small to deliver power to devices faster than their batteries discharge. Currently, the PZT film is quite small, measuring in at 21 mm long by 12 mm wide by 175 micrometers thick. The scientists suggest that if they double the area of the film, that would double the PENG’s current. They believe increasing the thickness of the film could increase the PENG’s current as well.

With a higher current PENG could be one day able to charge small devices. With the successful test of powering a small LCD and LED, it looks like the practical applications of the PENG are more than just a hopeful hypothesis.

Research paper: DOI: 10.1021/nl303755m – “Pyroelectric Nanogenerators for Driving Wireless Sensors”

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