Harnessing Body Heat as a Power Source for Batteries

For several years now, flexible thermoelectric devices have promised us that one day, futuristic equipment will be able to convert the heat emitted by the human body into electrical energy in order to power our portable electronic equipment such as connected watches or smartphones.

However, until now, the solutions explored in research and development centers were not flexible enough to be comfortable to wear and had a high manufacturing cost. So many obstacles to a commercial outcome for the general public.

A flexible, efficient and inexpensive thermoelectric film

But things could change thanks to the work of a team of researchers from the Queensland University of Technology in Australia. They have developed a flexible thermoelectric film that solves the problems of flexibility, manufacturing complexity, cost and performance.

“ Flexible thermoelectric devices can be worn comfortably on the skin where they efficiently convert the temperature difference between the human body and the surrounding air into electricity », explains Professor Zhi-gang Chen, who led this research project, the results of which were published in the journal Science.

The innovation is based on the use of a much less expensive manufacturing technique for a thermoelectric film covered with bismuth telluride crystals which produce a Peltier effect (thermoelectric cooling).

Screen printing and sintering

“ We have created an A4 size printable film with record thermoelectric performance, exceptional flexibility, scalability and low cost, making it one of the best flexible thermoelectric films available “, explains Professor Chen.

With his team, he used solvothermal synthesis, a technique that forms nanocrystals in a solvent under high temperature and pressure. It was combined with screen printing, which allows large-scale film production, and sintering which heats the films to a point close to melting, thereby bonding the particles together.

Enough to power a connected watch

In the tests carried out, the researchers say they obtained a power output of 1.2 milliwatts per square centimeter using a temperature difference between the skin and the air-facing sides measured at 20 kelvins.

“ The energy generated by the flexible thermoelectric film we created wouldn't be enough to charge a smartphone, but should be enough to keep a smartwatch running », Estimates Zhi-Gang Chen. According to him, the prospect of a thermoelectric bracelet for a connected watch is possible. “ It would take some industrial engineering and optimization, but we can definitely make such a smartwatch bracelet “.

Other possible applications

Besides generating power, the technology could also be used to cool electronic chips, allowing smartphones and computers to operate more efficiently.

It could power personal thermal management equipment in the form of a portable heating, ventilation and air conditioning system. The researchers also discuss the possibility of using this thermoelectric film to replace batteries for heart rate, temperature or movement sensors.