As reported in the journal Nano Letters, the material is a thin film made from a combination of multi-walled carbon nanotubes and polyvinylidene fluoride. While carbon nanotube/polymer composites are known to exhibit thermoelectric effects, the researchers discovered that they could generate more voltage by layering the film: the thermoelectric voltage generated was the sum of contributions from each layer, which considerably boosted the thermoelectric conversion efficiency.
The resulting material resembles humble felt in appearance and texture, which led the researchers to call it “Power Felt.”
Until now, thermoelectrics have been a tantalizing technology for powering all sorts of devices, but has remained largely untapped in commercial markets because of a lack of suitable materials. Existing materials either displayed poor thermoelectric conversion efficiency or were prohibitively expensive for commercial use. For instance, bismuth telluride, one of the materials most often used in commercial thermoelectric products like mobile refrigerators and CPU coolers, can cost as much as $1000 per kilogram. In contrast, the Wake Forest researchers expect that Power Felt would only cost $1 to add to a cell phone cover.
“Imagine it in an emergency kit, wrapped around a flashlight, powering a weather radio, charging a prepaid cell phone,” says David Carroll, director of the Center for Nanotechnology and Molecular Materials and head of the team leading this research. “Literally, just by sitting on your phone, Power Felt could provide relief during power outages or accidents.”
It seems there still is some question as to whether the Power Felt can actually generate enough current to power some of the items they’ve put on their list of potential applications. At present, seventy-two stacked layers of the carbon nanotube/polymer thin film can produce 140 nanowatts of power. So the researchers are looking into ways of adding more layers to the material to generate more.
Perhaps the answer is not just in boosting the power output of the thermoelectric material, but reducing the power consumption of the devices.
Last year I reported on work at the University of Illinois’s Beckman Institute for Advanced Science and Technology in developing a system that uses carbon nanotubes to control bits and lower power switching in phase change materials. At the time, one of the expected results of that work was that cell phones could be manufactured so that they consumed so little energy they could be powered by merely harvesting the thermal or mechanical energy from the environment.
Power felt may provide just such a cost-effective method for harvesting that thermal energy.