Simply by touching a small piece of Power Felt – a promising new thermoelectric device developed by team of researchers in the Center for Nanotechnology and Molecular Materials – Corey Hewitt has converted his body heat into an electrical current. Currently, 72 stacked layers in the fabric yield about 140 nanowatts of power. The team is evaluating several ways to add more nanotube layers and make them even thinner to boost the power output.
Comprised of tiny carbon nanotubes locked up in flexible plastic fibers and made to feel like fabric, Power Felt uses temperature differences – room temperature versus body temperature, for instance – to create a charge.
Potential uses for Power Felt include lining automobile seats to boost battery power and service electrical needs, insulating pipes or collecting heat under roof tiles to lower gas or electric bills, lining clothing or sports equipment to monitor performance, or wrapping IV or wound sites to better track patients’ medical needs.
“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. “Literally, just by sitting on your phone, Power Felt could provide relief during power outages or accidents.”
Cost has prevented thermoelectrics from being used more widely in consumer products. Standard thermoelectric devices use a much more efficient compound called bismuth telluride to turn heat into power in products including mobile refrigerators and CPU coolers, but it can cost $1,000 per kilogram. Like silicon, researchers liken its affordability to demand in volume and think someday Power Felt would cost only $1 to add to a cell phone cover.
Graduate student Corey Hewitt works with a sample of thermoelectric fabric in the Nanotechnology lab.
Nanoletters – Multilayered Carbon Nanotube/Polymer Composite Based Thermoelectric Fabrics
Currently Hewitt is evaluating several ways to add more nanotube layers and make them even thinner to boost the power output.
Although there’s more work to do before Power Felt is ready for market, he says, “I imagine being able to make a jacket with a completely thermoelectric inside liner that gathers warmth from body heat, while the exterior remains cold from the outside temperature. If the Power Felt is efficient enough, you could potentially power an iPod, which would be great for distance runners. It’s pretty cool to think about, and it’s definitely within reach.”
Thermoelectrics are materials capable of the solid-state conversion between thermal and electrical energy. Carbon nanotube/polymer composite thin films are known to exhibit thermoelectric effects, however, have a low figure of merit (ZT) of 0.02. In this work, we demonstrate individual composite films of multiwalled carbon nanotubes (MWNT)/polyvinylidene fluoride (PVDF) that are layered into multiple element modules that resemble a felt fabric. The thermoelectric voltage generated by these fabrics is the sum of contributions from each layer, resulting in increased power output. Since these fabrics have the potential to be cheaper, lighter, and more easily processed than the commonly used thermoelectric bismuth telluride, the overall performance of the fabric shows promise as a realistic alternative in a number of applications such as portable lightweight electronics.
Thermoelectrics at Wake Forest University.
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